A server rack system for managing power supply is provided. The system includes: a first LAN switch, a plurality of servers, at least one power supply unit, and an IMM. The first LAN switch is coupled to a management network. Each of the servers has a BMC. The BMC has a management network port connected to the management network. The power supply unit supplies electric power to the server rack system and has a management network port connected to the management network. The IMM has a management network port connected to the management network, visits the BMCs through the management network to acquire a power consumption value of the servers, generates a control command according to the power consumption value of the servers, and transmits the control command through the management network to the power supply unit. The power supply unit adjusts electric power output according to the control command.