A power management system includes connection interfaces, a system power supply, and a power management circuit. Each connection interface is connected to one power consumption device. The system power supply includes power supply units (PSUs). The system power supply supplies electricity power to each power consumption device via one connection interface. The power management circuit is connected to each power consumption device via the connection interfaces. The power management circuit obtains a current total load of PSUs, determines a target load of each PSU, and determines whether each connection interface is connected to one power consumption device. The power management circuit turns off power supply to the connection interface that is not connected to the power consumption devices. According to the current total load and the target load, the power management circuit determines an enabled number of the PSUs, thereby turning on or turning off each PSU accordingly.