I've got a weird one for ya. I have 2 usb plug chargers for my GNex. The Samsung wall charger that came in the box and the no-name dual ac/car adapter that came with the Costco accessory pack.
-Samsung wall charger: I get Charging (AC), no matter which of the 2 usb cables I use.
-AC/Car adapter and the cable that it came with, I get charging (AC) regardless if I'm plugged in to the wall or my car.
However, I can't use this to transfer any data to/from my computer, only charge. (Forgot to see check if this reports USB or AC... will check when I get home.)
-AC/Car adapter & cable that came with the Samsung wall charger. Reports Charging (USB) with the ac/car adapter, regardless if it's AC or Car. Reports Charging (USB) from all the USB ports on my laptop. However, I have a usb port that will charge accessories while the computer is off as long as it's plugged into the wall. This will report Charging (AC) and as soon as I turn on my computer, it goes to Charging (USB). The "charge when off" port is the only one that will report Charging (AC) and again, only when the computer is off. This is the only cable I have that works with data transfer.
-As a side note, I tried the data cable from a friend's Bionic and my computer wouldn't recognize my phone. So again, the only cable I've successfully been able to transfer data with is the Samsung cable. And the the only way I can get Charging (AC) from that cable is if a) my computer is off, or b) I carry my Samsung wall charger with me... unfortunately, this defeats the convenience of having the dual charger.