Obviously the cable works so it isnt a driver or windows 10 issue, He mentions he lost power, not the cable.
ONLY possible item I see with the cable(s) is intermittent connections, say a loose wire or so.
I recall had a 396XT while programming, a few thousand into programming(about 1/3-1/2 way) through programming it would stop. The problem was the original cable, not the adapter. I had another original cable and swapped it out and its been fine since.
If its intermittent, what I would do is place the cable, scanner on a flat surface, then run the updater, once it sees the scanner, start it again, but dont move nothing, including yourself!
Ive done a LOT of these updates, a few dozen, probably more. I recall one scanner had a blue screen only, just reran the updater, it took the update fine. That what I suggest retry, retry, etc.
Yes using just the one cable would rule out if the adapter cable has an issue. Finding an old pc with a com port would be running an older version of windows, hopefully windows 7 as that would work but a pc with comm port means it would likely predate windows 7. You could install windows 10 on it but the license would likely be to out of date, I recently updated a donated wiped clean pc with windows vista for the humane society here to windows 10 using "media creator tool". The license for vista it had was too old. Would it allow install of freescan, drivers on an unlicensed version of windows?
I recall having an old laptop of my brothers that had windows xp on it, ran freescan, but needed I believe the scenario was that the .NET version available wasnt available that freescan needed or something like that. Essentially couldn't get it to work.