It is really dependent on the environment and devices it is supporting. This is a link to a UPS Selector tool - http://www.dellups.com/disclaimer.asp (Click on "Start UPS Configuration" link)
You can configure it and then see what UPS would fit your needs the best.
Let me know if this helps.
Thanks for your response, Chris. The environment is Windows 2008 and the only device supported is the server itself, with the possibility of
adding the internet modem and router. In your opinion, would 3750W UPS be way more than we would?
Run through that configuration tool. UPS's vary based on wattage and runtime, so it depends on if you want it to maintain the server for another 5 minutes or an hour and a half etc.
3750 watts, a lot for a server, that could take on 5 servers and a few more devices, A unit this size is pretty expensive and so will replacement batteries. The advantages, your equipment as described will stay up a long time, and you should have a longer interval before replacement batteries are needed.
Been purchasing BBU's for over 25 years, I will not purchase new retail, due to the price and half dead batteries on arrival. I purchase refurbished units from the link below, units always come with fresh batteries. BBU don't die easily, so a new retail won't get you any more life versus a refurbished unit
This is a 2200 watt, I can place 3 server, a couple switches, monitor, a firewall and Internet router on it, and it will stay up at least 25 minutes