Here are some tips on purchasing and using an uninterruptible power supply (UPS) from my experience. These are devices allows a computer to keep running for a short time when the main electricity goes down. Many also provide protection from power surges. I would recommend buying one that did both as with current prices it is not worth buying it separately, and if you need a UPS, you will need a surge protector too.
UPS are funny things, I have seen ones that last for years and some that failed in a week. There is no pattern. Sometimes you can get a lemon, and they do not always work, I have seen computers and monitors damaged even though they had a UPS protection. It like everything is a 95% solution rather than a total solution.
As a rule, the real killer of UPS is the battery. Once the battery fails, you will need to decide whether to get a new one or replace the batteries. If you choose to get a new UPS, then you can still use the UPS as a surge protector. As a surge protector, they are useful for printers.
The first point you need to establish is how long do you need a battery backup, some places in the bush, electricity can be knocked out for hours while often in the cities, five minutes is plenty. As a general rule, most people look for about twenty to forty minutes. If the power is getting a bit long what you can do is disconnect some of the equipment from the UPS to give the battery less of a load.
Some points to look for in a UPS are
I do not like the plastic cases, retail shops are rugged and dirty places and it is over the years going to get pushed around. Get something that can take punishment.
Today we can never get enough USB charging ports as we are now forever always charging mobile phones, so you may as well get one that has a few USB ports.
Make sure that it produces an unmodified sine wave, some computer equipment does not like the power in a modified sine wave, that some UPSs deliver.
Have a quick look at the manual to see if it is readable. Many now have online manuals, and I prefer that as its always available then.
I would not worry too much about the integrated software that now many UPS have that can talk to your computer, I am a sceptic as I have never seen in all years anyone using this software much. Once it is plugged in the UPS, most people just want to forget about it.
Check as some UPS in operation are noisy. I find it very annoying if you have this constant buzz in the background.
What to do
Do not plug the printer into your UPS with a computer, in fact, anything mechanical. These can set up power spikes that can affect the computer and nothing in a computer that likes this.
Once you install a UPS, after a day when it should be charged up, I suggest pulling out the plug and test how long it goes. Since a UPS does not give you much of a warning if it fails, it is a good idea to pull out the plug once every few months to give it a test.
Do not put the UPS if possible too close to the computer, I have seen some UPS that cause static that makes a buzzing noise in the computer. Just moving the UPS away from the computer stopped this buzzing noise.
Much of the cost is in the batteries, and battery life varies greatly, sometimes they last only weeks sometimes years. Please keep the UPS in a cool spot. The odds are that you will get more life out of your battery as temperature dramatically affects battery life.
Hope this helps