Tuan Le
printWiFi and printUSB use the USB charging cable supplied with mobile device. Simply connect the mobile device's charging cable to the mobile device and the other end to the printWiFi or printUSB instead of the AC charging adapter. An additional benefit of this configuration, printWiFi or printUSB will charge the mobile device at the same time it charges its own battery. see the User Guide at http://www.imagetechcorp.com/support.html for additional details.