Let me ask you a few questions first:
- Has your UPS been in service more than 2 years?
- Have you replaced the computer since the UPS was installed?
- Have you upgraded the computer since the UPS was installed?
- Is your UPS missing an AVR circuit?
What size do I get?
OK. This involves some simple addition. Gather all the power requirements for all the devices for which the UPS will be insuring continuos power. Generally, this would be you computer box and the monitor. If you would like to include your modem and router, you can. Specifically you need to get the Watt rating for each of the devices. Once this list is complete, add it up. Your target UPS should be able to handle more than the total. Do not round down!
What is AVR and why do I want it?
AVR stands for Automatic Voltage Regulator. The AVR circuit allows the UPS input voltage within a certain range and output a steady constant voltage without the use of the installed battery. In most cases acceptable input voltage ranges from 90 to 140 volts. When the voltage is less that optimal, the regulator uses the steps up the voltage at the cost of a few amps (don't worry you have plenty.) When the voltage is a little over optimal, the regulator steps the voltage down adding to the available amps. An AVR circuit is to power what the suspension system is to an automobile. What this means to you is the UPS can handle most power fluctuations without engaging the battery and this is very good.
Is AVR pricey?
Well, a UPS with AVR does usually cost more than a comparable UPS without. However, recently the price gap has closed somewhat. For instance, at the time of writing, a Tripp Lite 300 watt UPS without AVR is priced at $59.99 and a Tripp Lite 300 watt UPS with AVR is $69.99. For the $10 difference, take the unit with AVR!
Should I consider anything else?
Yes, if you like to leave your computer on 24 hours/day you need to get a unit with a data cable and software. This combination will allows the computer to shut itself down automatically during an extended power outage.
That's it! Go forth with this knowledge and protect your computer from bad power!