This is a list of USB power supplies / charging devices that I own. I measured how they tell connected devices that they are for power supply only. This is done with the data lines (D+: green, D-: white).
|Google Nexus 4||5.0 V||1.2 A|
|Apple iPad 4||5.2 V||2.4 A||Model A1401 Flextronics LPS 0012ADU00|
|TP-Link TL-MR3020||5.0 V||1.0 A||HuntKey Model HKA00605010-3B|
|EasyAcc Wall Charger||5.0 V||5.0 A|