POWER SUPPLY APPARATUS

A plurality of systems of power supply circuits are provided between a power source and a load and are capable of cooperatively supplying power to the load using power of the power sources. In the power supply circuits, ground lines connected to a negative pole of the power source are configured independently for each system. A plurality of ground current detectors detect ground currents that are currents flowing through the ground lines of each system. The control units have ground line diagnosis portions that diagnose an abnormality in the ground lines based on the ground currents. When the ground line diagnosis portions determine that at least one system ground line is abnormal, the control units change the operation of the power supply circuit of the system determined to be abnormal.