The USB spec identifies different types of charging ports based on the resistance / voltage connected to the data pins. Here's a chart with the USB spec (on the

The USB spec identifies different types of charging ports based on the resistance / voltage connected to the data pins. Here's a chart with the USB spec (on the ends) and a couple manufacturer variants: http://i.stack.imgur.com/gWODO.jpg http://i.stack.imgur.com/gWODO.jpg