For starters, the MOS Reach outputs the standard 5 Volts DC which is compatible with all USB devices. The Reach outputs a maximum combined current of 3.1 Amps, which is shared between both USB ports. As you plug in devices to be charged, the devices will regulate how much power they draw up to their maximum charging capacity. Having more amps available than your USB device normally charges with will not hurt your device. If your two devices plugged in are capable of charging at currents higher than a total 3.1A, they will not be able to charge at their maximum speed, but this will not hurt your devices, or the MOS Reach. The maximum output wattage of the USB ports is 15.5 Watts (Watts = Volts X Amps).