Notwithstanding any other provision of law, all purchases and contracts made by the administrator or the Secretary of the Army for supplies or for services except for personal services, shall be made after advertising, in such manner and at such times, sufficiently in advance of opening bids, as the administrator or Secretary of the Army, as the case may be, shall determine to be adequate to insure notice and opportunity for competition. Such advertisement shall not be required, however, when (1) an emergency requires immediate delivery of the supplies or performance of the services; or (2) repair parts, accessories, supplemental equipment, or ser