A UPS (uninterruptible power supply) is a device that sits between a power supply (such as a wall outlet) and a device (such as a switch) to prevent outages, sags, surges, and bad harmonics from adversely affecting the performance of the device.
A UPS traditionally can perform the following functions:
Absorb relatively small power surges.
Smooth out noisy power sources.
Continue to provide power to equipment during line sags.
Provide power for a period of time after a blackout has occurred.
In addition, some UPS devices or UPS-plus-software combinations provide the following functions:
Automatically shut down equipment during long power outages.
Monitor and log power supply status.
Display the voltage (current draw) of the equipment.
