It's a backup power supply to which you connect. In the event of a power
failure in your area, this devices, known as a UPS or uninterruptible power
supply, kicks in and gives you a chance to save your work and safely shut
down your system.
There are several such units on the market, the following site is one
manufacturer and has a lot of information on the subject: www.apc.com.
UPS (Uninteruptable Power Source) for the home user that has batteries
in it.Normally it runs off the utility electrical outlet in the home.
When there is a power failure the UPS switches to the batteries and
keeps the computer running long enough to save any files that are in use
and perform an orderly shutdown.
I have an APC UPS for home use. You can find more info at their website:
