If you only need it to skip the power outage, I would look at something in the range of 800W to 1000W in an online ups.

This wattage should run your devices for 5 minutes or so, as you have quoted them. The online UPS will always run its load off on the battery, so there is no swap over time. Other types will be fine for a PC or normal electronics, but the hitch in power could cause a defect in the 3D print.

This is absolutely the correct information. I sold UPSs for years and the general consensus is that if you want more than 5 to 10 minutes of power, then you want to go with an actual generator solution

Saying that, UPSs tend to be used in industrial environments to keep machinery running until the generator starts up and can accept the load.