Exhibit 10(dddd)

PRIVILEGED AND CONFIDENTIAL

April 28, 2014

Energy Future Holdings Corp.

Energy Future Intermediate Holdings Company LLC

Energy Plaza

1601 Bryan Street

Dallas, TX 75201

Ladies and Gentlemen:

Reference is made to the Restructuring Support and Lock-Up Agreement, dated as of April 28, 2014 (the “Restructuring Support Agreement”), by and among Energy Future Holdings Corp. (“EFH”), Energy Future Intermediate Holding Company LLC (“EFIH”), and certain of their affiliates (collectively, the “Debtors”), the other parties thereto, and parties listed on the signature pages hereto (the “Initial Commitment Parties”), and the term sheets and other documents attached to the Restructuring Support Agreement, pursuant to which EFH and EFIH intend to engage in a restructuring of their existing liabilities in accordance with the Bankruptcy Code (the “Restructuring”). Capitalized terms used in this letter agreement and not otherwise defined herein shall have the meanings provided in the Restructuring Support Agreement or the Restructuring Term Sheet attached thereto (subject to Section 2 of the Restructuring Support Agreement).

The Restructuring contemplates, among other things, that the Commitment Parties and the Selected Partners, if any (as defined below), will, severally and not jointly, backstop a second lien subordinated secured debtor-in-possession note facility in accordance with the terms of the Second Lien DIP Notes Term Sheet (as defined below) (the “Second Lien DIP Facility”) that consists of (a) non-amortizing notes in an amount up to $1,900,000,000 (the “Tranche A Notes”) and (b) non-amortizing, non-interest-bearing notes issued in full satisfaction of the Funding PIK Fee (as defined below) (the “Tranche B Notes” and, together with the Tranche A Notes, the “Second Lien DIP Notes”). The Debtors will offer the right to purchase the Tranche A Notes to (i) Holders of General Unsecured Claims Against the EFIH Debtors (such Tranche A Notes, the “Tranche A-1 Notes”), subject to ratable reduction from participation by Selected Partners (as defined below), if any, in an aggregate amount not to exceed $400,000,000 and (ii) General Unsecured Claims Against EFH held by Fidelity (such Tranche A Notes, the “Tranche A-3 Notes”), subject to the conditions set forth in the Restructuring Support Agreement and the term sheet attached hereto as Exhibit A (the “Second Lien DIP Notes Term Sheet”) .

Upon the Effective Date, the Second Lien DIP Notes shall be subject to conversion to Reorganized EFH Common Stock (the “Equity Conversion”), on the terms set forth in the Restructuring Support Agreement, the term sheet attached hereto as Exhibit B (the “Equity Conversion Term Sheet”), and the Conversion Agreement (as defined in the Equity Conversion Term Sheet).

To provide assurances that the issuance of the Second Lien DIP Notes will be consummated, the Initial Commitment Parties hereby, severally and not jointly, commit to backstop the Second Lien DIP Notes in the respective percentages set forth on Schedule I hereto, on the terms and conditions described herein (including in the Second Lien DIP Notes Term Sheet and the Equity Conversion Term Sheet) and the Restructuring Support Agreement; provided, however, that the aggregate amount of such backstop shall not exceed $1.9 billion ($1,900,000,000) (the “Investment Commitment”). The Required Commitment Parties (as defined below) may from time to time (in their sole discretion), up to the date of funding of the Second Lien DIP Facility, select certain partners to transfer the Participation Rights to or to participate in the Investment Commitment in an aggregate amount not to exceed $400,000,000 of the aggregate Investment Commitment, in each case on prior written consent of EFH and EFIH unless such party is included on Schedule III hereto (the “Selected Partners”); and any such inclusion of Selected Partners by the Required Commitment Parties shall ratably reduce each Commitment Party’s portion of the Investment Commitment; provided, however, that such Selected Partner shall execute a joinder to this letter agreement, the Restructuring Support Agreement (in accordance with Section 4.04 thereof), and any applicable definitive document for the Second Lien DIP Notes; provided, further, that if a proposed transfer to a Selected Partner were to cause a Commitment Party to transfer more than 50% of its portion of the Investment Commitment (when taken in the aggregate with all other transfers of such Commitment Party’s portion of the Investment Commitment in accordance with the below), then the Required Commitment Parties may choose to (x) reduce the amount of the Investment Commitment to be transferred to the Selected Partner to an amount in which such Commitment Party would no longer be transferring 50% (in the aggregate) of its portion of the Investment Commitment or (y) cancel the contemplated transfer of the Investment Commitment. In addition, an Initial Commitment Party may in its sole discretion select a Selected Partner, or other party otherwise consented to by EFH and EFIH (the “Transferee Commitment Parties”) to purchase all or a portion of an Initial Commitment Party’s portion of the Investment Commitment; provided, that, with respect to an affiliate Transferee Commitment Party, the transferring Initial Commitment Party’s obligations with respect to the transferred portion of the Investment Commitment shall remain; provided, further, all Transferee Commitment Parties shall execute a joinder to this letter agreement, the Restructuring Support Agreement (in accordance with Section 4.04 thereof), and any applicable definitive document for the Second Lien DIP Notes; provided, further, if such transfer were to cause such Initial Commitment Party to transfer more than 50% of its portion of the Investment Commitment (when taken in the aggregate with all other transfers of its portion of the Investment Commitment by such Initial Commitment Party), such proposed transfer shall be deemed null and void ab initio. Subject to the foregoing, following any such sale or transfer by an Initial Commitment Party of all or a portion of its Investment Commitment, such Initial Commitment Party’s obligations with respect to such sold or transferred Investment Commitment shall cease. No Commitment Party other than an Initial Commitment Party shall be permitted to transfer any portion of the Investment Commitment. For purposes of this letter agreement, (i) the term “Commitment Party” shall mean, collectively, the Initial Commitment Parties, the Selected Partners, and the Transferee Commitment Parties, and Schedule I hereto shall be updated accordingly to account for any additional Commitment Parties and (ii) the term

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“Required Commitment Parties” shall mean, at any relevant time, three (3) Initial Commitment Parties (other than a Defaulting Commitment Party) that manage and/or advise funds or accounts that beneficially own, collectively, at least 66.6% of the Investment Commitment. Notwithstanding anything to the contrary contained herein, the identity of each Commitment Party shall be reasonably acceptable to the Borrowers.

In consideration for the Investment Commitment and on the terms set forth in this Commitment Letter and the Restructuring Support Agreement, EFIH shall (A) pay Pro Rata based on the respective percentages set forth on Schedule II hereto an amount in cash equal to 0.46% of $1.9 billion ($1,900,000,000) to the Initial Commitment Parties (the “Execution Fee”), which such Execution Fee shall be paid upon execution of this letter agreement, (B) subject to entry of the Approval Order, pay Pro Rata based on the respective percentages set forth on Schedule II hereto an amount in cash equal to 0.54% of $1.9 billion ($1,900,000,000) to the Initial Commitment Parties (the “Approval Fee”), which Approval Fee shall be paid within 5 days of entry of the Approval Order, (C) subject to entry of the Approval Order and the funding of the Second Lien DIP Facility, pay GSO and Avenue an arranger fee of $1,000,000 each in cash (the “Arranger Fees”), which Arranger Fees shall be paid within 5 days of entry of the Approval Order, (D) subject to entry of the Approval Order and the funding of the Second Lien DIP Facility, pay Pro Rata based on the respective percentages set forth on Schedule I hereto an amount in cash equal to 1.0% of $1.9 billion ($1,900,000,000) to the Commitment Parties (the “Funding Cash Fee”), which Funding Cash Fee shall become due and be paid in full by EFIH simultaneously with the funding of the Second Lien DIP Facility, and (D) issue Pro Rata based on the respective percentages set forth on Schedule I hereto an amount equal to 5.00% of $1.9 billion ($1,900,000,000) to the Commitment Parties in the form of Tranche B Notes (the “Funding PIK Fee” and, collectively with the Execution Fee, the Approval Fee, the Arranger Fees, and the Funding Cash Fee, the “Commitment Fee”), which Funding PIK Fee shall become due and be paid in full by EFIH simultaneously on the funding of the Second Lien DIP Facility. EFH and EFIH agree that the Commitment Fee and the Alternative Transaction Fee shall be nonrefundable once paid on the terms set forth in this letter agreement and that the Commitment Fee, the Alternative Transaction Fee and any other payments hereunder shall be paid without setoff or recoupment and shall not be subject to defense or offset on account of any claim, defense or counterclaim. For the avoidance of doubt, the Approval Fee, the Arranger Fee, and the Alternative Transaction Fee shall not be paid to any Defaulting Commitment Party.

If and to the extent that any one Commitment Party or multiple Commitment Parties do not satisfy its or their obligations in respect of its or their Pro Rata portion of the Investment Commitment (each such Commitment Party, a “Defaulting Commitment Party”), then each of the remaining non-defaulting Commitment Parties (the “Non-Defaulting Commitment Parties”) shall have the right, but not the obligation (the “Default Purchase Right”), to assume all or a portion of the Investment Commitment that was to be funded by such Defaulting Commitment Party (the “Defaulted Investment Commitment”). To the extent that the Non-Defaulting Commitment Parties (in the aggregate) desire to assume more than the total amount of the Defaulted Investment Commitment, then such Defaulted Investment Commitment shall be allocated among the Non-Defaulting Commitment Parties electing to assume the Defaulted Investment Commitment Pro Rata based on the respective percentages set forth on Schedule I hereto; provided, however, that if a Non-Defaulting Commitment Party is a Selected Partner, then such Non-Defaulting Commitment Party may only assume such portion of the Defaulted

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Investment Commitment so as not to exceed $400,000,000 of the Investment Commitment (calculated with all other Selected Partners). Each Defaulting Commitment Party shall immediately pay to each Non-Defaulting Commitment Party that elects to assume all or a portion of the Defaulted Investment Commitment, any portion of the Execution Fee, Approval Fee, and Arranger Fee received by such Defaulting Commitment Party, directly or indirectly, based on such Non-Defaulting Party’s Pro Rata share of the Defaulted Investment Commitment so assumed by such Non-Defaulting Commitment Party. For purposes of the Commitment Percentages set forth on Schedule I hereto, the Commitment Percentage for each of the Non-Defaulting Commitment Parties electing to exercise the Default Purchase Right shall be adjusted accordingly to reflect the reallocation of the Defaulting Commitment Party’s Commitment Percentage among the Non-Defaulting Committing Parties electing to exercise the Default Purchase Right (such that the total Commitment Percentage for the Non-Defaulting Commitment Parties shall equal 100%). In the event that the entire Defaulted Investment Commitment is not assumed by the Non-Defaulting Commitment Parties, the Required Commitment Parties may assign to a Selected Partner all or the remaining portion of the Defaulted Investment Commitment and following such assignment, Schedule I shall be accordingly adjusted as set forth in the immediately foregoing sentence.

Whether or not the transactions contemplated hereby are consummated, but subject to entry of the Approval Order, the Commitment Parties (other than any Defaulting Commitment Party and their respective affiliates and representatives, the “Indemnified Parties”) shall be indemnified and held harmless by EFH and EFIH, on a joint and several basis, from and against any and all losses, claims, damages, liabilities and expenses as a result of a claim by a third party, which any such Indemnified Parties may incur, have asserted against it or be involved in as a result of or arising out of or in any way related to this letter agreement, the matters and transactions referred to herein, the proposed Investment Commitment contemplated hereby, the use of proceeds thereunder or any related transaction or any claim, litigation, investigation or proceeding relating to any of the foregoing, regardless of whether any of such Indemnified Parties is a party thereto, and to reimburse each of such indemnified persons for any legal or other expenses incurred in connection with any of the foregoing from the date of the execution of this letter agreement until the termination of this letter agreement (for the avoidance of doubt, any claim for indemnification made after termination of this letter agreement for any event arising prior to the termination of this letter agreement shall not thereafter be barred and all claims for indemnification hereunder shall survive until finally resolved); provided, however, that the foregoing indemnity will not, as to any indemnified person, apply to losses, claims, damages, liabilities or related expenses to the extent they have resulted from the bad faith or willful misconduct of such indemnified person (as determined by a court of competent jurisdiction in a final and non-appealable judgment). The terms set forth in this paragraph shall survive termination of this letter agreement. This letter agreement is not assignable (a) by either of EFH or EFIH, without the prior written consent of the Required Commitment Parties (and any purported assignment without such consent shall be null and void ab initio), or (b) by any of the Commitment Parties, except to (i) its affiliates, subject to the terms and conditions contained herein (provided that such Commitment Party shall remain liable hereunder) or a Transferee Commitment Party as set forth above and (ii) the Commitment Parties may assign all or a portion of the Commitment Parties’ obligations hereunder to the Selected Partners as set forth above. This letter agreement is intended to be solely for the benefit of the parties hereto and is not intended to confer any benefits upon, or create any rights in favor of, any person other than the parties hereto.

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The obligations of the Commitment Parties to fund the Investment Commitment are conditioned upon satisfaction of, inter alia, each of the conditions set forth herein, in the Restructuring Support Agreement and in the Second Lien DIP Notes Term Sheet.

This letter agreement shall terminate upon the termination of the Restructuring Support Agreement. Subject to entry of the Approval Order, if EFIH enters into definitive documentation with respect to a reorganization, restructuring, merger, consolidation, share exchange, rights offering, equity investment, business combination, recapitalization or similar transaction (including the sale of all or substantially all of the assets of EFH, EFIH, or any other Debtor) involving EFIH on equal or better terms and conditions for EFIH than those contemplated in the Restructuring Support Agreement and the Term Sheet (such transaction, an “Alternative Transaction”), the Debtors shall pay Pro Rata based on the respective percentages set forth on Schedule II hereto, an amount in cash equal to 3.00% of $1.9 billion ($1,900,000,000) to the Initial Commitment Parties (the “Alternative Transaction Fee”), which Alternative Transaction Fee shall become due and be paid in full within 5 days Bankruptcy Court approval of such Alternative Transaction. For the avoidance of doubt, the Alternative Transaction Fee shall not become due or be payable if the Debtors consummate an Alternative Transaction because of the failure of the Commitment Parties to fulfil their obligations under the Investment Commitment.

All rights and remedies provided in this letter agreement are cumulative and not exclusive of any other rights or remedies that may be available to EFH, EFIH, and the Commitment Parties, including (without limitation) all rights to specific performance, or as otherwise provided by law, equity, statute, or in any other agreement entered into in connection with any of the transactions contemplated hereunder, including as to any Defaulting Commitment Party.

Upon execution of this letter agreement, EFH shall or shall cause EFIH to promptly pay (i) Akin Gump Strauss Hauer & Feld LLP, by wire transfer of immediately available funds, an advance payment of $3,000,000 (the “Akin Gump Advance Payment”) and (ii) Centerview Partners LLC, by wire transfer of immediately available funds an advance payment of $675,000 (the “Centerview Advance Payment,” and together with the Akin Gump Advance Payment, the “Advance Payment”). In accordance with the terms of that certain amended and restated engagement letter with EFIH dated April 27, 2014 (as may be amended or modified from time to time, the “Centerview Engagement Letter”), EFH shall or shall cause EFIH to promptly pay Centerview an aggregate arrangement payment of $5,000,000, which shall be paid as follows (x) $1,250,000 shall be paid upon the execution of this letter agreement (the “Arrangement Payment I”), (y) $1,250,000 shall be paid simultaneously be paid within 2 days of entry of the EFIH Second Lien DIP Order (the “Arrangement Payment II”) and (z) $2,500,000 shall be paid simultaneously with the funding of the Second Lien DIP Notes (the “Arrangement Payment III,” and together with the Arrangement Payment I and Arrangement Payment II, the “Arrangement Payment”). Upon entry of the Approval Order, EFH and EFIH agree to pay, within 15 business days of delivery of an invoice (which shall include reasonable supporting detail, which may be redacted to protect privileged or confidential information), the unpaid reasonable and

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documented fees and expenses of Akin Gump Strauss Hauer & Feld LLP, pursuant to that certain engagement letter with EFIH dated May 24, 2013 (as may be amended or modified from time to time), Centerview Partners LLC, pursuant to the Centerview Engagement Letter and, without limitation, all other out-pocket fees, costs and expenses of the Commitment Parties, including the fees and expenses of the Commitment Party Professionals incurred previously or in the future relating to the Restructuring or the Chapter 11 Cases, pursuant to applicable engagement letters entered into between such professionals and EFH or EFIH, as applicable (such fees and expenses, the “Professional Fees”). Payment of the Advance Payment, the Arrangement Payment and Professional Fees shall not be subject to allowance by the Bankruptcy Court; provided, however, that EFH and EFIH shall promptly provide copies of invoices received on account of the Professional Fees to the U.S. Trustee and counsel to any Committee appointed in the Cases, and the Bankruptcy Court shall have exclusive jurisdiction over any objections raised to the invoiced amount of the Professional Fees, which objections may only be raised within 15 business days after delivery of an invoice(s) therefor. In the event that within 15 business days from delivery of such invoices EFH, EFIH, the U.S. Trustee, or counsel to the Committee raises an objection to a particular invoice, and the parties are unable to resolve such objection, the Court shall hear and determine such dispute; provided that payment of invoices shall not be delayed based on any such objections and the relevant professional shall only be required to disgorge amounts objected to upon being “so ordered” pursuant to a final order of the Bankruptcy Court. EFH and EFIH agree that the Advance Payment, Arrangement Payment and Professional Fees shall be nonrefundable and that the Advance Payment, Arrangement Payment and Professional Fees and any other payments hereunder shall be paid without setoff or recoupment and shall not be subject to defense or offset on account of any claim, defense or counterclaim. Notwithstanding anything to the contrary herein, the Debtors shall not be obligated for any of the professional fees or other obligations described in this paragraph incurred after this letter agreement terminates.

This letter agreement shall be governed by, and construed in accordance with, the internal laws of the State of New York, without giving effect to the principles of conflict of laws that would require the application of the law of any other jurisdiction. By its execution and delivery of this letter agreement, each of the parties hereto hereby irrevocably and unconditionally agrees for itself that any legal action, suit or proceeding against it with respect to any matter under or arising out of or in connection with this letter agreement or for recognition or enforcement of any judgment rendered in any such action, suit or proceeding, may be brought in either a state or federal court of competent jurisdiction in the State of New York. By execution and delivery of this letter agreement, each of the parties hereto hereby irrevocably accepts and submits itself to the nonexclusive jurisdiction of each such court, generally and unconditionally, with respect to any such action, suit or proceeding. Notwithstanding anything to the contrary herein, upon the commencement of the Chapter 11 Cases, each of the parties hereto hereby agrees that, if the petitions have been filed and the Chapter 11 Cases are pending, the Bankruptcy Court shall have exclusive jurisdiction over all matters arising out of or in connection with this letter agreement. EACH PARTY HERETO UNCONDITIONALLY WAIVES TRIAL BY JURY IN ANY LEGAL ACTION OR PROCEEDING REFERRED TO ABOVE.

This letter agreement may not be amended or waived except in a writing signed by EFH, EFIH, and the Initial Commitment Parties. Notwithstanding the foregoing, this letter agreement

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may be amended by the Initial Commitment Parties to add Selected Partners and Transferee Commitment Parties as Commitment Parties in accordance with the terms of this letter agreement. This letter agreement may be executed in several counterparts, each of which shall be deemed to be an original, and all of which together shall be deemed to be one and the same agreement. Execution copies of this letter agreement may be delivered by facsimile, electronic mail or otherwise, each of which shall be deemed to be an original for the purposes of this paragraph.

Notwithstanding anything contained herein, each Initial Commitment Party acknowledges that its decision to enter into this letter agreement has been made by such Commitment Party independently of any other Commitment Party.

This letter agreement (including the exhibits and schedules hereto), along with the Restructuring Support Agreement (including the exhibits and schedules thereto), constitutes the entire understanding among the parties hereto with respect to the subject matter hereof and replaces and supersedes all prior agreements and understandings, both written and oral, between the parties hereto with respect to the subject matter hereof, and shall become effective and binding upon (i) the mutual exchange of fully executed counterparts by the EFH and EFIH and all of the Commitment Parties, and (ii) payment by EFH or EFIH of the Execution Fee, the Advance Payment, the Arranger Fee, and the Arrangement Payment I in accordance with the above.

[SIGNATURE PAGES FOLLOW]

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If the foregoing is in accordance with your understanding of our agreement, please sign this letter in the space indicated below and return it to us.

Signature page to letter agreement.

THE FOREGOING IS HEREBY

AGREED TO AND ACCEPTED:

EXHIBIT A

Second Lien DIP Notes Term Sheet

Execution Version

ENERGY FUTURE HOLDINGS CORP.

ENERGY FUTURE INTERMEDIATE HOLDING COMPANY LLC

SECOND LIEN SUBORDINATED SECURED DEBTOR IN POSSESSION NOTES FACILITY TERM SHEET

Capitalized terms used but not defined herein shall have the meanings set forth in the letter agreement, dated as of April 29, 2014 (the “Commitment Letter”), to which this Term Sheet is attached, or the Restructuring Support Agreement (as defined in the Commitment Letter).

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EXHIBIT B

Equity Conversion Term Sheet

Execution Version

ENERGY FUTURE HOLDINGS CORP.

EQUITY CONVERSION TERM SHEET

Capitalized terms used but not defined herein shall have the meanings set forth in the letter agreement, dated as of April 28, 2014 (the “Commitment Letter”), to which this Equity Conversion Term Sheet is attached, or the Restructuring Support Agreement (as defined in the Commitment Letter).

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