I have had trouble free motoring from my trusty old 1995 Legacy up until this morning...

On my way to local shop I noticed wipers running a lot slower then normal..bucketing with rain here in Ireland. Came out of the shop and found my battery flat..! Its a new battery so I am looking at Alternator issues..have not put a meter on it yet as I have to boost charge the battery first. I decided to pop up to our local breakers yard where there is a 1996 Legacy Wagon that is for parts, bought the alternator on the off-chance it needs to be replaced.
Shock horror I notice the little plug in socket is totally different to the one on my car. Its a little rectangular socket and the one on my car is circular...
My legacy is an import (USA I think) and i may have problems getting the correct replacement.
Any advice on where I can purchase some service exchange Alternators, and are alternator failures common on this model...(silly question I suppose) I am hoping its a battery, or perhaps a fuse which I will check later.
Cheers and thanks for any assistance
Regards
Paul