My daughter bought some of those cheap knock-off chargers, and now at least 1 of 3 have failed. It gets hot with nothing plugged into it, and does not charge anything. This is not a counterfeit, since they haven't tried to look exactly like an Apple cube, but it's probably the same circuit as those counterfeit units.

I popped it open to take a look. Other than the smell of hot electronics, not much was obvious. I eventually noticed that the small zener diode on the USB board (last photo) was not soldered on one end, and its leads had not been clipped short. They may have caused a short to something nearby. I fixed that. No change.

I've also found that the optoisolator near that zener gets wicked hot very fast after plugging the cube in. I could replace that part but it's probably not worth it?

Anybody know how these things work?

 

Here is an example from a 12 volt wall wart. I have seen similar circuits that were lacking the opto isolator.




edit: I just noticed that yours has the opto.