An Uninterruptible Power Supply (UPS) is a stand-alone energy source that supplies emergency power when the main power source fails.

Unlike a redundant power supply, an uninterruptible power supply is a stand-alone device that is not a part of any other device or system. Its sole purpose is to provide continuous power, even during an outage. UPS units differ from auxiliary systems or emergency generators in that they provide seamless protection from power disruptions by 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 UPS devices is fairly short, but it allows enough time for a secondary power source to come on line.

UPS backups are generally used to safeguard computers, data centers, telecommunication equipment or other electrical devices where an unanticipated power interruption could lead to business disruption or data loss.