[bell-cot]

Not an expert, but...

What does the manufacturer of the dialysis machine recommend? (Either specific brands/models, or generalities about the quality of power needed by their machines.)

In many areas, "power failure, and resident needs power for a home medical device" is a situation that the local Fire Dept. / EMS / Utility regularly handles, or has protocols for. I'd check with them. If nothing else, if things really went sideways and they were responding to your FIL's home, having a UPS that they were familiar with could be a real benefit.

[nitred]

Just got back a reply from the manufacturer that they cannot recommend any UPS. They clarified the specs the UPS should have which is 1200VA + sine wave + 120V.

[bell-cot]

D*mn! ...but 100% understandable, from a liability PoV.

Though I might still be tempted to ask them if they could anti-recommend any UPS's. Saying that they heard of someone using a FooBar X2400, but it didn't end well, could still be useful. Especially if you'd tentatively decided on a FooBar X2400.