A power supply protecting apparatus includes a first comparison unit, a second comparison unit, and a switch unit. The first comparison unit receives an input voltage from an electronic device, compares the input voltage with a first DC voltage, and outputs a first control signal. The second comparison unit receives an output voltage from an electronic device, compares the output voltage with the first DC voltage, and outputs a second control signal. The switch unit receives the first control signal and the second control signal, and outputs a first voltage level reference voltage when receiving a first voltage level first control signal from the first comparison unit or a second voltage level second control signal from the second comparison unit. A reference terminal of the electronic device receives the first voltage level reference voltage, and the electronic device stops working when receiving the first voltage level reference voltage.