The invention relates to a switching power circuit connected to a motherboard of a computer system. The switching power circuit includes a PWM circuit and a snubber circuit. The PWM circuit includes a phase terminal, and it may output an output voltage to the motherboard via the phase terminal. The snubber circuit includes a zener diode. A negative terminal of the zener diode is connected to the phase terminal, and a positive terminal is connected to the ground terminal. The level of a breakdown voltage of the zener diode is equal to the level of the output voltage in a steady state.