The invention provides a power supply for a computer mainframe, which is cooled by a heat conduction method, and more particularly to a power supply without a cooling fan. The present invention features a highly effective heat pipe connecting a plurality of aluminum-extrusion heat sink fins and a plurality of aluminum-extrusion heat sinks, the aluminum-extrusion heat sink fins fixed above a cooling chip over a circuit board, and the aluminum-extrusion heat sinks fringed near the power supply, with a part of the heat sink fins exposed to the power supply. The heat of a chip is conducted out of the power supply by the aluminum-extrusion heat sink fins, the high-effect heat pipe, and the aluminum-extrusion heat sinks. Therefore, the power supply can reach an expected cooling effect without the cooling fan.