I'd be suspicious of the regulator. Somehow it is probably hard over
causing the alternator to go to full output. It isn't the fault of
the alternator that it is hardover. If anything I'd guess the
alternator is OK.

Jump starting is sometimes a complicated art. Yeah, the plug thing
will get things rotating, but a couple of times on Cessnas I've found
that afterwards the alterator wouldn't turn on. The schematics showed
a lot of isolations between the two systems - just why I don't know.

Read your flight manual carefully and study any schematics that might
be applicable.