Dedicated charging ports exist, they can be recognized by having something like zero Ohm, or respectively 200 Ohm between D+ and D-, or 15k Ohm on each pin agai

Dedicated charging ports exist, they can be recognized by having something like zero Ohm, or respectively 200 Ohm between D+ and D-, or 15k Ohm on each pin against ground. (See also Maxim's USB Battery Charging survival guide) That is, "power only" cables are not recognizable to the user, and malicious chargers came into being for that reason.