U

UL Underwriters Laboratories. An approval organization based in the United States.

Uninterruptible Power System (UPS) A system designed to automatically provide power, without delay or transients, when the normal power supply is incapable of supplying acceptable power. Some UPSs also filter and/or regulate utility power.

UPS Topology Overall term describing the internal circuitry of a UPS. There are three basic UPS topologies: standby (off-line), line-interactive, and online.

User-Replaceable Batteries User replaceable batteries allow the user to easily exchange UPS batteries, once the unit has been turned off.