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The uninterruptable power supply (UPS) is a battery backed-up unit. Most smaller units do nothing more than monitor the incoming voltage. Typically, when the voltage gets down into the 92-95 volt range is when the trip point takes over and goes on battery. Most smaller units are what are actually termed as EPS or emergency power supply. This states that the equipment you are powering actually runs on line votage until it drops to the trip point and then switches over to battery power.

A true UPS works just the opposite. Your equipment, ie. computer, etc., runs off the baterry while the line votage keeps the battery charged. Thus, the filtered or 'clean' voltage to your equipment. When line voltage drops, your equipment does not see any type of blip in incoming power. The EPS's have an ever so slight 'blip' when the power shifts. Electronics have made this 'blip' extremely minimal. But, if you look closely enough you could possibly see the change over. Some equipment today has power supplies that help even out this 'blip', but if it is too long, that is when the damage can get done.

Look on the boxes of the items that you are looking to purchase and they will state on there whether they are 'line conditioning' or 'line filtering' or something of that nature.

One thing to consider when making your decision on size of UPS. Some of the larger ones, in the 500 watt range, have line filtering. Line filtering will help better and keep a consistent voltage to your equipment. While the UPS will give you back up power, the smaller ones will not 'clean' the incoming voltage. You will still have the spikes and drop-outs that may have caused your equipment failure.

Just something to consider. I would pay the extra 20-40 bucks for the line filtering, even if it meant getting a bigger than needed unit. (you can always find stuff to plug into it)

Just my $.02. ymmv