Ken Shirriff embarked upon a teardown of counterfeit Apple laptop chargers. On the outside, they're typo-free and very convincing. Inside, though, they're a dangerous mangle of cheap parts and inexplicably bad decisions.
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The most important feature of a charger is the isolation between the potentially-dangerous AC input and the low-voltage output… The counterfeit MagSafe charger has a dangerously small distance between the low voltage side (top) and the high voltage side (bottom). This is why you shouldn't buy counterfeit chargers.
I'm puzzled as to why counterfeit chargers never manage to have sufficient clearance distances. They use simple, low-complexity circuits so the circuit board layout should be straightforward. Except in the smallest cube phone chargers, they aren't fighting for every millimeter of space. It shouldn't take much additional effort to make the boards safer.