The cable probably was carrying mains voltage. Most of the cheap third-party chargers have very poor clearances inside, and tend to skimp on protection. It's no

The cable probably was carrying mains voltage. Most of the cheap third-party chargers have very poor clearances inside, and tend to skimp on protection. It's not that rare for them to end up with a 5V DC atop a 120/240V AC mains. The phone will often still charge just fine, but the cable is dangerous. Also, depending on the resistance as little as 10mA can be dangerous. That would mostly be wet or abraded skin, 100mA is a more general value for dangerous currents. But USB can charge at 500mA to 4A or so, depending on the version. It's only the low voltage and high resistance of skin that limits the current.