A power supply system includes a power supply, a daughterboard, and a motherboard. Output currents of power connectors of the motherboard and impedances of copper foils between every two adjacent power connectors of the motherboard are obtained via simulation. A voltage of one power connector of the motherboard is predetermined. Therefore, desired impedances of copper foils between VRM connectors and corresponding power connectors on the daughter board are determined via calculations, to make currents passing through the power connectors of the motherboard equal to each other.