It is not recommended to plug laser printers in to a UPS. Laser printers consume a lot of power during normal operation and especially at the initial time the fuser warms up. This large consumption of power can easily overload a UPS. Laser printers should be plugged directly into the wall socket. The power supplies on laser printers are designed for this use.
If you have a Back-UPS it is also not recommended to plug the laser printer in to the surge protected outlets. The power the laser printer consumes could have adverse affects on the rest of the protected equipment, even on the battery back up up side of the UPS.
If you really need to put a laser printer on a UPS, then you need to size the UPS properly to accommodate the large power consumption of the laser printer. Check with the manufacturer to find out exactly how much wattage the laser printer consumes during printing, and how much voltage is consumed during the initial warm up stage. You’ll need a Smart-UPS, large than a Smart-UPS 1500VA. Don’t be surprised if you end up needing a Smart-UPS 2200VA or a Smart-UPS 3000.