7.5W is a wireless charger.
Wireless charger is the use of electromagnetic induction principle of charging equipment, its principle and transformer similar, through the sending and receiving end of each placed a coil, the sending end of the coil under the action of power to the outside electromagnetic signal, the receiving end of the coil received electromagnetic signal and electromagnetic signal into the current, so as to achieve the purpose of wireless charging. Wireless charging technology is a special way of power supply, it does not need the power line, rely on electromagnetic wave propagation, and then the electromagnetic wave energy into electricity, and finally achieve wireless charging.