A power supply circuit for south bridge chip includes a voltage conversion chip, a control circuit, and a voltage increasing circuit coupled electrically to the voltage conversion chip and the control circuit. The voltage conversion chip is configured for outputting a driving signal. The control circuit is configured for receiving the driving signal and a first voltage, and converting the first voltage to a second voltage according to the driving signal. The voltage increasing circuit is configured for increasing voltage level of the second voltage, wherein the second voltage is supplied to the south bridge chip via the voltage increasing circuit.