What is UPS

UPSUninterruptible Power SupplyUPS is a hardware device that provides a backup power source in case of a power outage (blackout), brownout, or a surge in power. A UPS provides enough power for the computer or computers to shut down properly or to remain up during a temporary power outage. Typically, a UPS keeps a computer running for several minutes after a power outage, enabling you to save data that is in RAM and shut down the computer gracefully.
Many UPSs now offer a software component that enables you to automate backup and shut down procedures in case there's a power failure while you're away from the computer. There are two distinct types of UPS: off-line and line-interactive (also called on-line).

An off-line UPS remains idle until a power failure occurs, and then switches from utility power to its own power source, almost instantaneously. An on-line UPS continuously powers the protected load from its reserves (usually lead-acid batteries), while simultaneously replenishing the reserves from the AC power.
The on-line type of UPS, in addition to providing protection against complete failure of the utility supply, provides protection against all common power problems, and for this reason it is also known as a power conditioner and a line conditioner.