Some backup power supplies also contain surge suppressors. The reset button of a backup power supply allows it to be reset after a power surge has triggered the surge suppressor. Within the housing is a transistor which is set at a certain, maximum line power. If the power exceeds this maximum, the transistor breaks the circuit, popping the small reset button out. After the line power surge has passed, the breaker may be reset. Some power supplies do not have a built-in surge suppressor and so rely upon a separate unit to suppress current fluctuations.
