Eaton is my recommendation. Look at the 5S1500 (modified sinewave) or 5SC1500. They all work with NUT. I have one of my UPS connected to a Raspberry PI Zero with NUT. And my servers NUT clients are scheduled to shutdown after a 2min outage and my NAS after 4min. I can also monitor the UPS from Home Assistant and receive notifications on my phone each time the UPS goes OB or OL.
Anything other than QNAP.