Like most things in life, you purchase from Ebay, second hand items, could be good, probable is, but could also be faulty. Lots of Chinese imports etc. with different standard for Resistors and surge protectors etc.
Amazon, less likely, alas I could not tell a good unit from a copy, so when yours arrives, just make sure it looks like yours and has same values for electrical components inside it, same thickness for wiring and quality of electrical joints etc. etc.
(just my view) 
In a completely sane world, madness is the only freedom (J.G.Ballard).
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