Stu, the thing about OEM alternators is that the gods must love them, they keep creating so many more kinds. Oh wait, no, maybe that's "better idiots" they keep making.
Either way, about the only thing we can be sure an anonymous "auto" alternator shares in common with the next one is that it is not designed to run at 100% power for long, and the internal regulator is designed to not overcharge a battery during long use. As opposed to charging one quickly.
Charging voltages, temperature protection, surge protection, many things vary from one to the next but if someone is working with limited time, or money, and has to upgrade one piece at a time, usually starting with "Oh damn, I need new batteries NOW" it may not be the best solution, but upgrading piecemeal can be made to work.