system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do USB chargers have all contacts in their ports? Why not just power and ground and omit data?
gpt
The specs for USB allow devices to pull 100mA prior to device negotiation. Great for small simple things like e-cigs. When you start getting into things like flash drives and smartphones, you're going to need more than that. In that case, your device will negotiate with the USB controller to determine the max current that the device will accept. That negotiation takes place over the data wire, like any other devices.