How does an Uninterrupted Power Supply work?

An Uninterruptible Power Supply (UPS) is a device connected between the power source and a computer to ensure that electrical flow is not interrupted. UPS devices use batteries to keep the computer running for a period of time after a power failure. It is not to be confused with standby generators which do not provide protection from a momentary power interruption, or which may result in a momentary power interruption when it is switched into service, whether manually or automatically. UPS devices usually provide protection against power surges, brownouts and line noise as well.