Some store / bench testers are "ok" and some aren't. The BEST way to test a charging system is "in the car" in which it is being used........as I mentioned earlier.......the "sections", the components, the output circuit, and the field circuit. Testing in-car can test the entire system as a whole.
Most bench testers don't have the horsepower to fully load a high output alternator. It takes a LOT of power to spin a say, 100a alternator up to full shaft output RPM
