An uninterruptible power supply (UPS) is a secondary source of electricity. It is an alternative source of electricity only conditionally, only for a limited time, depending on the battery capacity and load. Unlike a power generator that requires the time to start up after a power outage, the UPS guarantees continuous power supply without any interruption. This feature sets it apart from other secondary and alternative power sources. Its advantage is that it improves the power quality of protected devices.