Abstract: A power supply for providing excitation to notification appliance circuits (NACs) in fire alarm applications meets revised national and international requirements for both NAC drive and auxiliary load drive tasks with a single circuit configuration. The requirements stipulate ability to tolerate inrush when activating strobe lights and horns of ten times the nominal output, while limiting short-circuit drive in AUX mode to eight amperes after five seconds. The novel power supply improves on the requirements, first by continuously testing for overcurrent NAC status and signaling faults in real time, and second by shutting off AUX drive in event of a short and retrying periodically without a requirement for manual reset. Thus testing for wiring errors is rendered safer and nondestructive, and correction of a wiring error can be quicker.