An uninterruptible power supply (UPS) is a system of electrical components to provide a buffer between utility power, or other power source, and a load that requires uninterrupted, precise power (e.g., a computer system, for the purpose of eliminating the effects of transient anomalies or temporary outages). This often includes a trickle-charge battery system which permits a continued supply of electrical power during brief interruption (blackouts, brownouts, surges, electrical noise, etc.) of normal power sources.
An UPS consists of an inverter, usually electronic, that is powered by a battery that is kept trickle-charged by rectified AC from the incoming power line fed by the utility. In the event of an interruption, the battery takes over without the loss of even a fraction of a cycle in the AC output of the UPS. The battery also provides protection against transients. The duration of the longest outage for which protection is ensured depends on the battery capacity, and to a certain degree, on the rate at which the battery is drained.