I've had good success w/ APC 'Smart UPS' or Cyberpower. The important thing is pure sine wave output as the cheap UPSs take shortcuts and often produce stepped sine wave approximations.
Figure out what the power draw and how long you need to run the device for. How do you plan on 'shutting it down properly'?
Most UPS's are not rated by how much power they can put out, but by how many amps they can put out at rated voltage multiplied by that voltage. regardless of the phase angle between the two. You can tell it's not power if the rating is in volt-amps and not watts.
Conversely, most devices that you'd want to connect to a UPS are rated in terms of the power that they draw.
How to sort that out?
If you knew the
power factor of each device, you could do sorting out with a little math, but it is quite rare for a device to specify its power factor. So you have to guess. It's fairly safe that a 1000 va UPS can drive a load of 700w. It's quite safe that it can drive a 600 w load. You can scale those numbers for other UPS ratings. But there are no guarantees, and YMMV.
Another thing to watch out for in inrush current when you first turn a device on or bring it out of sleep state, but that is not usually a problem with inkjet printers. It is a major problem with electrophotographic -- aka laser -- printers.
Jim