Folks have been complaining about "rebuilt" starters, alternators, water pumps, etc. for as long as I can remember. This ain't new. Folks were bitching in the 1970s when the parts were rebuilt in the USA.
If you think "rebuilt" parts are bad news, wait til you try "brand new" (Made in Communist China) junk. At least the rebuilt stuff starts with quality castings and "used to work" acceptably; the "new" crap has zero service history and you're lucky if the Chinese drilled all the holes in the proper places, then threaded all the holes they were supposed to.
Half the problem with "faulty" rebuilts is the vehicle they were installed on; or the guy doing the work. Either the guy missed that the vehicle wire harness was cooked, or the real problem with the alternator was a failed battery or parasitic drain from the clock; or he installs the wrong part, or he installs the proper part incorrectly, or he decides to "test" the new alternator by disconnecting the battery with the engine running so he can see if there's a "proper spark" and pops one or more diodes in the "new" alternator, making it defective. I've known guys who replace an alternator with failed bearings, then stretch the belt so tight you could play it like an instrument. Then they wonder why the "damned rebuilt" locks up on it's bearings.
HINT: If you're not testing the battery for Open Circuit Voltage (OCV) and cold-cranking amps, If you're not testing the starter for current (amperage) draw, and if you're not testing the old--and the new--alternator for regulated voltage at fast idle, regulated max current at fast idle, full-field voltage, and full-field current, and if you're not testing alternator voltage drop from output at the alternator to + battery post, and the ground stud on the alternator (or alternator case) to - battery post...and then checking for parasitic draw, and proper belt tension, you haven't properly diagnosed and installed the alternator. In other words, the alternator, starter, battery, regulator (if external) and the wire harness that connects all these parts is a system that has to work together. If any one part fails, other parts may fail in a chain-reaction. So just because the alternator is dead, doesn't mean replacing it fixes the root cause of the failure--which might be a failed wire harness or a failed battery.
[Edit]Forgot to mention testing for AC voltage "Ripple" from the alternator, too.[/Edit]