Inductive coupling in one paragraph
The charger contains a transmitter coil driven by alternating current, which creates an oscillating magnetic field. The phone's receiver coil sits in that field and converts it back into current, which the phone regulates into its battery. No electrical contact exists; the air gap - through glass backs and thin cases - is part of the circuit. Efficiency depends on how tightly the coils couple, which is why distance and alignment dominate real-world performance.
Alignment: the hidden specification
Two coils offset by a few millimetres couple poorly: charging slows, heat rises. Magnetic alignment systems (the MagSafe pattern and the magnetic designs in the Qi ecosystem) solve this mechanically - magnets snap the phone into the coil's sweet spot. That is why the manufacturer's foldable stations are magnetic: the 3-in-1 series uses magnet alignment to keep the phone position honest on a desk or in a hotel room. When you evaluate samples, test with the phone deliberately misaligned; the difference between a good and a bad magnetic design shows immediately.
Why 15W wireless is not 15W wired
The 15W figure is the receiver-side maximum under aligned, cool conditions. Part of the transmitted energy is lost in the coupling itself, and phones taper power as they fill and warm. Expect a 15W wireless station to deliver a full charge noticeably slower than a 15W wired connection - the honest comparison is in wireless vs wired charging. What wireless buys is not speed but behaviour: one motion, no cable wear, a tidy desk. The manufacturer's line publishes its ceiling plainly - 15W maximum on every model from the core models to the 5-in-1 stations - with input requirements (9V/3A class) printed beside it, because an under-powered adapter is the most common cause of “slow wireless charging” complaints.