PX-W4012TU vs PX-W4012TA

I don't know for sure with those specific models, but I would guess that there's not really any tangible difference. My experience with the behavior of other Plextor drives makes me think that the U model is probably just the internal drive inside of a USB enclosure.

For example, I have a Plextor Premium internal drive. However, I only use it as an external drive over USB, as it's connected to a machine with no PATA ports. When I run Plextools Professional XL, it identifies the drive as a Premium-U (despite the label on the drive showing the model as just a regular Premium).

Should be functionally identical, yes.

I recall seeing a post from some years back over on MyCE where someone stated that Plextors are fussy about external cases / USB to PATA adapters. That's not been my experience, though. Despite the Redump Wiki recommending otherwise, I've just been using whatever cheap no-name USB to PATA / SATA adapters I had laying around when I started dumping, and the Plextors have been fine with it. I've even able to use Plextools to control drive settings when the drives are connected via these cheap adapters. That being said, if I was buying an adapter today instead of just using what I happen to have on hand, I'd go with a Ugreen or Kingwin or similar, as going that route probably minimizes the chance of issues compared to the generic ones I ended up using. (Especially since, IIRC, there used to be warning in the Wiki stating that some of the crappy generic adapters may brick drives. I didn't see that warning until after I'd been using my cheap adapters for a year already, or I probably would've ordered some nicer adapters when I was starting off. At that point, I just stuck with my crappy adapters, because I kinda figured if they were gonna brick the drives it woulda happened by then.)

Not directly related here, but I have had issues with some SATA to USB adapters in the past. I had an issue with a drive would work fine for reading via my generic SATA to USB adapter, but, if trying to burn a disc, the adapter would stop communicating with the drive in the middle of the burn until I unplugged and replugged the adapter. A nicer adapter solved that problem. In any case, that was with a newer LG drive and not a Plextor.