1 wire internal or external oem alternator
Ok. So right now, today, there isn’t a local parts house within an hour of my house that has an OE Mopar alternator on the shelf. You’d be waiting a day, or spending most of your day driving. And if you’re stranded somewhere with a dead alternator you can’t do that anyway. If you’re not you can wait a day.
Are there places that have them? Sure. Could I find the 1 wire powermaster with a serpentine pulley I run in stock on the shelf somewhere? Probably not. Would a denso that’s more likely to be on the shelf fit in a pinch? Maybe. But not every town you might break down in will have an OE Mopar alternator on the shelf anymore.
I also haven’t had a new powermaster alternator die on me (yet). But I have had the woefully underpowered stock Mopar alternators crap out. And a couple voltage regulators too. Got those on the shelf local too?
For me it’s moot, even the largest OE alternator at 65 amps probably wouldn’t run my electric fans and the rest of my car at the same time.
Which to get back to the OP, is a consideration for a build. Because if you’re going to run a more modern set up - fuel injection, electric fuel pump, electric fans, stereo, AC, etc etc, you may not be able to run an OE alternator just on amperage demands. And I’d rather have my car built the way I want it than to hamstring my build with an OE part that might not be on the shelf when/where I need it anyway.
Really, the time when having OE parts on a 70’s Mopar meant you’d be able to walk into a random local parts shop and walk out into the parking lot and fix your car has passed. Sometimes it might work. Sometimes it definitely wouldn’t.