[microtonal]

It is probably hard to say, from the outside they often look legit. I have seen one once, but it became more apparent when we compared it to a genuine charger (usually the print is off in some way). Since counterfeit chargers typically have fewer components, apparently weighting the charger can also help finding counterfeits:

https://www.electricalsafetyfirst.org.uk/blog/how-to-spot-a-...

Of course, it's probably not beyond them to add some weight to make you believe it is real.

I guess if you have the right tools, you could also measure output quality.

[lloeki]

They do add weight (and go through the trouble of implementing ring structures to fake writes)

https://youtu.be/g8ovFkd8myE