Many iPad associated adapters only put out a total of 2.1 amps. The PowerLine product provides 2.1 amps per port for a total of 4.2 amps. Other similar products may not FAST charge an iPad at the same time that it is charging an iPhone, let alone charge TWO iPads simultaneously. If the product is not designated as a Made for iPad/iPhone/iPod, the charger’s electronics also may not contain the passive logic that tells the iPad it is capable of FAST charging so it may not FAST charge an iPad at all. A simple way to think of this is as follows: a computer USB port offers 500 mA of charging power. An iPad will slow charge when it is in its OFF position while connected to a computer. IF the iPad does not see 2.1 amps and the correct resistor settings from the USB power source, the iPad slows the charge like in a computer’s USB port. To FAST charge an iPad it requires 2.1 amps and the correct resistor from a USB charging port. Other multi USB port chargers can’t FAST charge the iPad if another device is also connected. ONLY the PowerLine Dual 2.1 amp Adapter provides both 2.1 amps and the resistor setting to FAST charge from EACH USB port (4.2 amps total).