A power source protection device and a power source protection method are disclosed herein. The power source protection device includes a power supply, a power source managing unit and a signal sending unit. The power supply provides a DC input voltage. The power source managing unit receives the DC input voltage, and when a determining voltage related to the input voltage is larger than a set voltage, enters a startup state and outputs a supply voltage. After receiving the supply voltage, the power source managing unit transforms the DC input voltage into a standby power output voltage and provides the standby power output voltage when the signal sending unit sends a control signal to the power source managing unit within an enabling time. VVhen it has not received the control signal within the enabling time, the power source managing unit enters a shutdown state.