https://www.youtube.com/watch?v=3DhyEmEu2ks

Few years ago I installed a used Ford 3G alternator from a Thunderbird. Max. amp output a full rpm was about 95 I recall.
Engine idling at 500rpm, Interior fan ON, headlights ON
13.1v charge.

Somewhere last year the 3G alt got replaced with a used later model nippondenso alternator and the same idle charge was maintained.

No need to spend big bucks on 'brand' alternators that are no better than (modern-ish) stock factory stuff.