Delete comment from: Ken Shirriff's blog
TL;DR
Check output voltage witch iStat. Fake had circa 17,5 V instead of circa 20 V.
I've met "genuine" Apple 85W adapter from Allegro (Polish ebay thing). I started feeling suspicious after opening the package: there was no original box or characteristic "rectangular" cord tape. Build quality was also not so Apple'ish. I've went to official Polish Apple service and there they couldn't say if the adapter genuine or not. After some research I've decided to measure the output voltage and I've installed iStat. In the app measurments said the output voltage is 17,5 V which was odd, because every adapter I've checked has circa 20 V output.
Luckily I returned it with full refund...
May 29, 2016, 9:40:01 AM
Posted to Counterfeit Macbook charger teardown: convincing outside but dangerous inside