An Uninterruptible Power Supply (UPS) is a device that supplies emergency power when the main power source fails.
An uninterruptible power supply differs from an auxiliary system or standby generator in that it will provide immediate protection from power distributions using one or more attached batteries and associated electronic circuitry for low power users, or diesel generators and flywheels for high power users. The runtime of most uninterruptible power supply sources is fairly short, but allows enough time for a secondary power source to come on line.
An uninterruptible power supply is generally used to safeguard computers, data centers, telecommunication equipment or other electrical devices where an unanticipated power interruption could cause injuries, casualties, business disruption or data loss. Uninterruptible power supply units range from being capable to guard a single computer without a video monitor to large units powering whole data centers, buildings, or cities.