under the heading Afghanistan Infrastructure Fund in prior Acts: Provided further , That such costs shall be limited to contract changes resulting from inflation, market fluctuation, rate adjustments, and other necessary contract actions to complete existing projects, and associated supervision and administration costs and costs for design during construction: Provided further , That the Secretary may not use more than $50,000,000 under the authority provided in this section: Provided further , That the Secretary shall notify in advance such contract changes and adjustments in annual reports to the congressional defense committees: Provided further , That the authority to provide assistance under this heading is in addition to any other authority to provide assistance to foreign nations: Provided further , That contributions of funds for the purposes provided herein from any person, foreign government, or international organization may be credited to this Fund, to remain available until expended, and used for such purposes: Provided further , That the Secretary of Defense shall notify the congressional defense committees in writing upon the receipt and upon the obligation of any contribution, delineating the sources and amounts of the funds received and the specific use of such contributions: Provided further , That the Secretary of Defense shall, not fewer than 15 days prior to obligating from this appropriation account, notify the congressional defense committees in writing of the details of any such obligation: Provided further , That the Secretary of Defense shall notify the congressional defense committees of any proposed new projects or transfer of funds between budget sub-activity groups in excess of $20,000,000: Provided further , That the United States may accept equipment procured using funds provided under this heading in this or prior Acts that was transferred to the security forces of Afghanistan and returned by such forces to the United States: Provided further , That equipment procured using funds