In a well-known incident in 2016, Apple sued a company making fake "Apple" power adapters, and in the suit alleged that 90% of the "Apple" products on Amazon were fake.

That such adapters are literally dangerous is clearly documented in Ken Shirrif's teardown:

http://www.righto.com/2014/05/a-look-inside-ipad-chargers-pr...

http://www.patentlyapple.com/patently-apple/2016/10/apple-su...

http://www.businessinsider.com/majority-apple-accessories-am...

https://lifehacker.com/how-to-spot-a-counterfeit-apple-light...