A computer system including a power supply and N main boards is provided, herein N is an integer greater than 1. The power supply generates a main power and a standby power. The N main boards respectively correspond to one standby voltage. The 1st to the (N-1)th main boards respectively generate the corresponding standby voltage by the main power in a power-on state, and respectively generate the corresponding standby voltage by the standby power in a power-off state. The Nth main board generates the corresponding standby voltage by the main power in the power-on and power-off state.