The system includes following modules: monitoring module in use for sending control signal in use for controlling on/off signals of all branches in power source system; rectification module in use for converting AC from power source to DC, which is output from bus; module of stand-by power supply in use for supplying power for load when AC is breaken; DC distribution module in use for dividing DC voltage into multiple voltages to provide the voltages to loads, and connecting to the module of stand-by power supply; being connected to monitoring module and DC distribution module, the control device is in use for controlling on/off of branches of module of stand-by power supply. Through turning on/off control signal for branches of module of stand-by power supply, the control device controls on/off between module of stand-by power supply and bus. Moreover, control signal of branch current is only tens to hundred mA so as to reach effect of safe operation.