There are some gray areas where opinions vary as to what's on-topic. Where you draw the boundary around "computer hardware" is one, and the context affects it.
I don't put a UPS in the same category as an electronic device. Those are generally devices that have their own, independent purpose. They become on-topic only to the extent that you are interfacing them with a computer. They temporarily become part of the computer "system" when they involve computer-based activity.
I see a UPS as a more or less essential part of the computer-related hardware. It's a permanent part of the hardware configuration and performs an important function in using the computer and preventing corruption. It also doesn't have an independent purpose. It's like an extension of the power supplies for the computer-related hardware. So I include it in the circle I draw around the computer system.
I suppose some other people might view this differently. The computer and related peripherals can be viewed as ending at their power cords. If you are in an area where utility power isn't reliable, you can improve the reliability of what comes out of the wall by adding a UPS. So the UPS is more of a peripheral for the utility company.
Part of the context is whether the question relates to computer operation/activity vs. repairing a device. There is generally a lot of latitude for the core components of the computer (computer and its input/output devices). Questions about maintaining or servicing those components are generally allowed as long as they don't get too far into the weeds and become questions about electronics and electronics repair.
A device that is on-topic only because it is being used with the computer won't generally be on-topic for questions about maintaining or servicing it. So if someone puts a UPS in that category, servicing it might be viewed as off-topic.
For questions that fall in the gray area, you're likely to find examples that were treated differently, depending on who saw them first.
Your question is about (maintenance) operation of the UPS, so if someone views a UPS as not a component of the computer system, it is understandable that they would view the question as off-topic. However, the function you ask about is controlled by computer-based software (APCUPSD). You do link to it in the question, but it may not be immediately obvious if the reader isn't familiar with it and doesn't follow the link. A reader who doesn't view the UPS as a computer component might also view APCUPSD as somewhat irrelevant because its purpose is to control the UPS, not something computer-centric.
The community can weigh in on gray area questions and vote to undelete and reopen (although if a moderator views the question as clearly off-topic, they can overrule the community input). For what it's worth, I'm in the camp that views the UPS as part of the computer, so I cast my single vote to reopen the question.