I own a Kubota M4700 tractor and when its alternator (built in regulator) died Kubota wanted many hundred$ of dollar$ for a replacement.
I bought one on Ebay for $69 and it came with excellent documentation and complete testing-data/results in 3 days with free shipping. (Shipped out of Dallas in fact.)
It has worked PERFECTLY and is IDENTICAL in every way to the OEM (Denso).
One thing the Chinese are very good at: COPYING. It is an EXACT copy and does the job.
(Also found an internal regulator by googling the Kubota PN for the regulator. Got one off Ebay for $16. Took about one beer to install, so now I have a spare alternator.)
Edit: Local alternator shop wanted $180 to replace that regulator and Kubota wanted $116 for the part.