I agree. It is very difficult even when we do know what the original rating was. Then that's complicated by Chrysler's alternator part numbering. Service part numbers were not always the same as the original, and the same alternator would be given a different number depending on which pulley it got.
Then for those of us with 'driver' cars there is the whole issue of 'ratings'. There seems to be no standard on how alternators are rated. On top of that rebuilders frequently substitute or mix up parts in a batch. Not just the pulleys but also the rotors and stators. :(