An uninterruptible power supply is a static device designed, firstly, to reserve (protect) the power supply of electrical receivers due to the energy stored in the battery and, secondly, to provide CE for protected electrical receivers.

The first and most important purpose of an uninterruptible power supply is to provide power to a computer system or other equipment at a time when the electric network cannot do this for some reason. During such a failure of the electric network, the UPS feeds itself and supplies the load due to the energy accumulated by its battery.