The utility model relates to a power supply device of a vehicle-mounted electronic device. The device mainly comprises a vehicle-mounted power supply unit, a voltage detection protecting unit and an electronic switch unit, wherein the voltage detection protecting unit is connected with the vehicle-mounted power supply unit and the electronic switch unit to detect voltage output by the vehicle-mounted power supply unit; when the detected voltage value is judged to be lower than a set too-low voltage threshold or higher than a set over-high voltage threshold, the voltage detection protecting unit sends a cutoff control signal to the electronic switch unit; the electronic switch unit is connected with the vehicle-mounted power supply unit and the voltage detection protecting unit; and when the electronic switch unit is in the cutoff state after the cutoff control signal is received, the voltage output by the vehicle-mounted power supply unit is transmitted to the vehicle-mounted electronic device, and the power supply for the vehicle-mounted electronic device is cut off. The power supply device of the vehicle-mounted electronic device, disclosed by the utility model, has the advantages of preventing damage of the vehicle-mounted device due to the damage of the power supply of the vehicle-mounted electronic device which is resulted from over-high voltage output by the automobile power source and unreliable working of the device due to too-low voltage output by the power supply of the vehicle-mounted electronic device which is resulted from too-low voltage output by the automobile power source.