Abstract: A computer system with an over-subscription mode of power-supplying device is provided. The computer system includes at least a power-consuming device, at least a power-supplying device, and a power management controller. The at least a power-supplying device supplies power to the at least a power-consuming device. The output power of the at least a power-supplying device has a maximum label value, a safety limitation value higher than the maximum label value, and an over-subscription zone between the maximum label value and the safety limitation value. The power management controller is coupled with the at least a power-supplying device and the at least a power-consuming device that controls the power consumption of the at least a power-consuming device. If the output power exceeds the maximum label value to enter the over-subscription zone, the power management controller will lower the power consumption of the power-consuming device(s).