I think you have managed to skirt around and discount the answer to your question. UPSs are not intended to be anything but a very short term power source. They are there to provide emergency power long enough to either shut down cleanly or migrate to another long term source of power. In your example with the “home power backup”, you have that and a UPS. The UPS smooths out the power and covers the few milliseconds during the transition. Even large datacenter UPS installations operate in this fashion. Datacenters would have a secondary source of power, typically diesel generators. The UPS batteries will be sized to run the site for a few minutes - enough time to get their generators up and running and the load transferred to them.

It got into the top ten music charts too iirc - and the bbc refused to play it on the chart countdown.

There seems to be a few publishers missing here …

• Baen books (https://www.baen.com/) have never applied DRM to their books.
• TOR (https://torpublishinggroup.com/) stopped DRM on their books about ten years ago.

Baen typically sells their wares directly but TOR are through the usual sellers but have no DRM. I’m not sure how this works in practise with Amazon’s new “you can’t get the files” policy, but they are probably in cleartext somewhere.