Low-voltage electric appliance power supply system and dual-power engineering machinery

The utility model relates to a power supply system, and provides a low-voltage electric appliance power supply system and a dual-power engineering machine in order to solve the problem of switching of power supplies of vehicle-mounted low-voltage electric appliances when the existing dual-power engineering machine uses different power sources. The switching power supply anode and the storage battery anode are respectively connected with the movable end of the selection switch through diodes; two ends of a first relay electromagnetic coil are respectively connected with the first fixed end of the selection switch and the cathode of the storage battery; two ends of a second relay electromagnetic coil are respectively connected with the second fixed end of the selection switch and the negative electrode of the switching power supply; the first end of the low-voltage electric appliance is connected with the positive electrode of the switching power supply through a first relay normally-closed contact and connecte