Abstract: A power supply has both high and low voltage power sources connected to a common output terminal. A switching circuit is connected between the high voltage source and this terminal, the switching circuit being controlled by a control circuit. The control circuit operates in response to malfunction and temperature sensors when these sensors have outputs indicative of equipment operating conditions outside of predetermined ranges for each of the sensed parameters. When the control circuit is not being actuated by an output from one of the sensors, the switching circuit is actuated to connect the high voltage output to the output terminal. In the event, however, that one of the temperature or malfunction sensors senses a condition outside of range, the control circuit is actuated, thereby deactuating the switching circuit to remove the high voltage output from the output terminal, leaving low voltage output.