Uninterruptible power supply
An uninterruptible power supply (UPS) is a device that allows a computer to keep running for at least a short time when incoming power is interrupted. As long as utility power is flowing, it also replenishes and maintains the energy storage. The more energy stored, the longer power can be maintained, with practical limitations that will be discussed later. The differences among UPS systems lies in the technology that enables them to do their jobs.
Different types of UPSes
The most commonly used type of UPS is also the most effective, generally called a full-time or full double conversion UPS. For any UPS, incoming utility power is alternating current (AC), which is also what is required by most information technology equipment (ITE). Batteries, on the other hand, are direct current (DC) devices, so all battery-type UPSes must convert -- or rectify -- the incoming AC power to DC to charge the batteries. The UPS must also still deliver AC to the ITE, so DC power must be converted back to AC through a device known as an inverter.