Bad cables will impede charging but not harm the alternator, unless they are shorted of course.
A disconnected alt will produce 14v but zero Amps.
Most probably it’s either a bad connection job or bad reconditioning job.
Measure the resistance of the cables to see if there is something wrong.
Running an extra earth wire between the engine and the chassis is always a very good idea.
If you end up needing a new alternator this might help: