3 Description: Protective circuit to prevent overcharging. Use your existing USB charge/ sync cable for charging. Dual USB AC adapter, charge two USB devices simultaneously. Simply plug it into an wall outlet and charge through a proper USB cable. To use it with any USB devices, simply connect a USB cable (not included) to your device and then to the charger module, easy to use. Compatible with most of the USB enable devices including Apple iphone, iPod, Microsoft Zune, cell phone, PDA, digital camera / camcorder and more. Attention: If you charge two devices simultaneously, then the 2.1 A current will be divided, so it is normal that it can't charge so fast as you charge only one device.