Regulator bad? for sure?

[data89]

I've suddenly found that my alternator is not charging. And why do these things always happen on a Sunday in the middle of nowhere?

Okay, so I had the alternator tested at Autozone and it tested fine. I assume, then, it has to be the voltage regulator. I pulled one I had saved off the shelf (I thought I had saved it because it was good) and installed it, but, still it would not charge. So, maybe it's bad too. The question is, if the alternator is good, is it for sure that the regulator is bad!

A new original is $38, and a compatible one is $22. I have used aftermarket parts like this with good success. Is a compatible regulator good enough? Either way, if it turns out the new regulator (whichever one) does not solve the problem, I'm out the money because you can't return it.

But, the problem has to be the regulator, right? (wiring and fuses are all good). 1969 C10 stepside, 250.