My experience has been that current UPSes tend to give a pretty limited runtime, more-limited than you might think, and are surprisingly-expensive for the capacity that they do provide.

The reason one historically really wanted a home UPS wasn't necessarily to run a machine through a power outage, but to provide time to save any work and shut that machine down. We used to use filesystems that could become corrupt if they weren't brought down cleanly. You could maybe run a machine for minutes, not many hours.

So it was important to warn (and maybe auto-shut down). UPSes are good at that. You have beeping alarms, software to auto-shut-down a machine cleanly when the battery gets low if someone isn't around, software to notify a single attached computer about the battery level.

But with the combination of filesystems that don't do that plus software that auto-saves, that's less critical. What I think most people want is just more runtime, having a shot at making it through short power losses.

I think that today, if I wanted to provide longer-running resistance to power outages, I'd probably look at one of two things:

• For a device or two, "power stations". These sometimes get called "solar generators", despite not generating anything, because manufacturers are marketing them as an alternative to gasoline/diesel generators for power outages. All-in-one box with batteries, charge controller, and inverter in one little case. This kind of thing. They won't beep to warn you that the power is out, and they won't have software (or interface) to tell a computer to automatically shut down.

• For larger capacity, a "grid tie solar system". These tend to be extensible, with separate 12V (or 24V or 48V) batteries or the like and separate boxes for the battery charge controller and inverter. You don't actually need to hook any solar panels or other power sources up to it (though, hey, maybe you decide that you want to do so), as the battery charge controller will charge the batteries from the grid as long as the grid is providing power. You can select a size for and replace the batteries and inverter and charge controller separately, and you aren't constrained to use a single vendor for all the components.

I would look to see that the inverter in question provides "pure sine" output. Some inexpensive inverters provide a square wave, and some devices don't much like this.

EDIT: Ah, just saw your new comment:

Power outages are usually very short (few seconds max).

You may not care about keeping the system running through longer outages, then, unless you're also worried about longer ones.