This has been discussed a few times already, but I'll explain again. The design of our original alternator is not the greatest. However, Denso, a Japanese company, builds these to exacting specifications and the quality of internal parts and workmanship is top notch. Due to that they perform well and tend to last ~100 - 150K miles. When they fail many of these original alternators become cores for companies that remanufacture alternators. They repair/rebuild them and sell as "remanufactured" units. When Denso does it the end product rivals the quality of a new alternator and will generally last as long as the original one did. When other companies do it they may or may not use quality parts and/or workmanship (more profit margin to use cheap parts and labor). Due to this, it's not uncommon to see inexpensive "remanufactured" units only last 10 - 20K miles.

Of course not all remanufacturers are the same. Some are going to be better than others. It's my guess that the cheap ones won't hold-up well but the more expensive ones will likely last a bit longer. Which ones are the best? I don't know (only time will tell). Here's a thread with more information:

https://www.toyotavantech.com/forum/...lternator-woes