There are three desktops which get used at my house, and at times all three are being used at the same time, so when there is a power cut all are disconnected from the electricity, but they need to be working even when there is a powercut. The solution I know ofcourse is getting a UPS, but which UPS can I get? Like I have mentioned I need all three desktops working and along with a tube light and a light bulb a ceiling fan as well, so which UPS will be most suitable to run all these devices?
You would need atleast a 2800Va UPS and I cant think of a better brand then APC. You have not mentioned how long the power cuts are in your area and how often so cannot comment on the kind of battries you should be using. If you could tell us how many hours back you are looking for then I would be able to advise about the battries as well.
Depending on how many hours you wish to run the desktops when there is a power cut its difficult to advise on the number of batteries. As an idea I would think that you would need at least 4 good quality batteries. As far as the brand for the UPS APC is the best.