late reply,, but
with your desktop it just needs ac power.
your chosen UPS system will become the new power source.the UPS takes in utility power then converts that AC to stored DC.
The stored DC is then converted to AC again and out to your machine. You can hand make a more reliable UPS with stuff you already have If you don't mind since I know your a can do guy.
The issue you have is utility feeder issues so not only will it kill sensitive electronics but the NEW appliances are also at risk of failure due to transients and Neutral current surges (momentary surges in current flow on your neutral leg) and with a ground rod outside reading greater than 100 ohms, replacing your home ground rod should be the first step in full facility protection. Next would be to upsize the physical ground wire from your meter base or sub panel and home run that to the ground rod with idealy a Cad weld but acorn fittings seem to be normal in shitty install applications (ie- everyone's home). so many people out there pay no or little attention to grounding.
Now that your ground is stable, your input to your chosen UPS can "suffer less" and may possibly be able to handle minor power issues like brown outs or intermittent phase voltage/current changes. The walmart variety UPS input circuit is somewhat sensitive to input power stability and you can only control so much. that's why I say that making your own UPS would be better because you can use older tech that would be able to absorb input power problems without overcomplicated TTL technology or switchmode power supply driven devises which are less capable of living through many input power problems.
a homemade UPS would look like this.....
-12v battery charger input sourced from your 120v outlet., you would want an older working charger because these are less sensitive to input power problems and can take a hit when it does happen.
-12v battery charger output tied to your 12v battery of choice & a on off switch on the red wire including a 5amp or 10Amp fuse... all in series
-12v battery posts bond to your inverter input red / black.
-inverter output outlet becomes your desktop input power.
--- when utility is on, depending on your charger type, ideally your charger is the primary inverter source for power... amps is everything.
--- when utlity is lost, the battery becomes the primary source and discharges upon the inverter and your still making power for a long time, enough time to wrap up and shut down If you want.
--- disadvantages are with 12v auto batts is H2 gas,, so a VRLA battery would be better, I personally would worry too much about a flooded cell battery in my house.
and ive been working along side your staff for longer and I will slightly contradict what you said ,,,,
It is possible for perfectly good hardware to crash just because oem firmware and / or software is no longer supported thus becoming what appears to be a broken device to the "new update"
Example, I had a win XP SP1 HP desktop that at some point several years ago I started getting IE messages and Google notifications that my system will no longer be supported soon. I stopped doing Win XP SP1 updates shortly after and eventually stopped doing updates at all because many updates are based on assumptions that you are buying new shit all the time and creating more planetary garbage. I kept my Malwarebytes account updated and it ran really strong and protect my old slow HP machine until a year ago I did an update... that very update crashed my machine and tech support at Malwarebytes actually confirmed it. End result was that the update I was doing was like putting a round peg in a square hole. Firmware is the biggest hassel and software updates follows second. Yes hardware fails be everyone be advised that those invisible little 1's and 0's can kill a perfectly good machine as well. The older the machine the less support and the more time you need to take to "step into" levels of firmware or software updates.
An external tera drive allowed me to keep all my files so the old HP became scrap parts.
I feel for the IT industry, I almost went that route for employment years ago and decided I didn't think it was a good fit for me so im in critical facilities power & construction which I design engineer for various telecom providers.