> If the charging device can use more current, nothing happens. That's not true -- if you put a power supply capable of supplying, say, 10 amps at the end of a

> If the charging device can use more current, nothing happens. That's not true -- if you put a power supply capable of supplying, say, 10 amps at the end of a wire rated for 0.5A, and then you connect a 10 amp device to that wire, the wire will get very hot and then melt. If this wire is on a circuit board inside a device, the resulting heat may destroy the components nearby and/or start a fire. If the wire is a USB cable, the cable and/or connector may melt. Most of the wires / traces in an computer or smartphone aren't capable of carrying the full amount of current that a battery or charger can supply. That's why protection circuits are required, and why USB 3 has a complicated negotiation process around how much power the bus-powered device can draw.