This invention provides a power supply comprising a mother board, a first socket, and a DC-DC converter module. The mother board comprises a transformer operative for transforming an input power into a first AC output power and a filter operative for receiving the first AC output power and filtering the first AC output power into a first DC output power. The first socket is mounted on the mother board and electrically coupled to a circuitry of the mother board by way of at least one conductor terminal operative for providing the first DC output power. The DC-DC converter module mounted on a printed circuit board electrically coupled to the mother board comprises a DC-DC converter operative for receiving the first DC output power and converting the first DC output power into a second DC output power and a third DC output power and a second socket operative for providing the second DC output power and the third DC output power by means of a conductive path of the printed circuit board. There are several advantages including the reduction of the use of the conductive wires, the improvement of the efficiency of the power supply, the simplicity of the circuitry of the power supply, and the easy replacement of the broken component because the DC-DC converter module is mounted on an individual printed circuit board different from the mother board.