The present invention relates to a feedback device for a power supply, including a main feedback module, an auxiliary feedback module and a feedback control module. The main feedback module is adapted to sample a voltage on a main output branch of the power supply, and output a main feedback voltage to the feedback control module. The auxiliary feedback module is adapted to reduce the main feedback voltage when a voltage on an auxiliary output branch of the power supply drops. The feedback control module is adapted to control the power supply to increase its power output when the main feedback voltage decreases, so that the voltage on the auxiliary output branch is restored to normal. By using the power supply feedback device of the present invention, the circuit is simple, not only solving voltage sag problems, but also ensuring the power density and cost.