$1 vs $50 Phone Charger. What’s the difference?

Faster switching reduces the number of transformer windings needed and lets the power electronics react instantly to live battery readings, so GaN-based chargers can squeeze more wattage into a smaller, cooler design without overheating the phone.

Gallium nitride switches can toggle roughly twenty times faster than silicon, which lets chargers run at much higher frequencies and therefore deliver more power in a much smaller package.

Chargers first rectify wall AC to DC so a semiconductor switch can pulse that DC into a high-frequency waveform, and that high-frequency signal lets a much smaller transformer and precise electronics produce the low-voltage output the battery needs.

A transformer’s step-down is set by the turns ratio between primary and secondary coils, and the operating frequency changes how efficiently the core couples those turns, so higher frequency can achieve the same step-down with fewer or smaller windings.

A transformer cannot work on DC because it needs the alternating current to create a changing magnetic field that induces voltage in the secondary coil, and DC produces no changing field so nothing is induced.

Batteries require steady low-voltage DC because wall electricity is high-voltage AC that flips polarity many times per second, and that reversing voltage cannot be stored by a battery without first being converted.