A power supply system includes a PWM power supply connected to and supplying power to a power-consuming unit and a power supply protocol management apparatus connected to the power-consuming unit through a transmission bus for acquiring a VID protocol of the power-consuming unit and acquiring a VID code conversion table matching the VID protocol. The power supply protocol management apparatus converts a VID code output by the power-consuming unit (on the basis of the VID protocol) into a required voltage of the power-consuming unit according to the VID code conversion table, compares the required voltage with a voltage at an output end of the PWM power supply to generate a feedback voltage value, and transmits the generated feedback voltage value to the PWM power supply which adjusts its output voltage according to the feedback voltage value.