An uninterruptible power supply (UPS), also known as a continuous power supply (CPS) or a battery backup is a evice which maintains a continuous supply of electric power to connected equipment by supplying power from a separate source when utility power is not available. It differs from an auxiliary power supply or standby generator, which does not provide instant protection from a momentary power interruption. Integrated systems that have UPS and standby generator components are often referred to as emergency power systems.