If you are referring to a uninterrupted power supply for a computer then you will want to consider the following: sufficient volt/amps to run the computer long enough to shut it down properly, a surge suppression system incorporated in the device with a high joule rating, and/or a supplemental surge protector plugged into the ups system, Line voltage regulation(this keeps the voltage at a normal safe level, steps up the voltage if it falls to low during brownout conditions,lowers voltage during high voltage conditions) hope this helps.