Abstract: A power supply structure is disclosed in which a base member has first and second sets of plug pin receiving openings with electrically conductive sockets behind the openings. Each first set is grouped with a second set, and the sets are provided with power from separate sources e.g. clean and contaminated power. Socket modules each of which includes electrically conductive pins can be plugged into the openings. Each socket module has plug pin receiving openings for receiving plugs on power leads. In one form each socket module is unplugged from the base member, turned through 180 degrees and plugged into the base member again to change from one type of power to another. In a further form the base member includes switches which provide power selectively to the socket behind the first and second sets of openings.