[danhor]

Most modern (GaN) USB-C chargers are already highly efficient. Since USB-C PD can only be used as a point-to-point connection (since a voltage level is negotiated), a sane architecture would likely use a high voltage (>100V to minimize resisitve losses) DC line with local step-down. At that point, the dc-dc step down shouldn't be integrated into the cabeling but into an external unit or into tne device, since the idle power, size and cost of a 500W PC power supply and a 5W headset charger is very different (even using DC).

The losses from the AC conversion aren't very high and the most energy intensive consumers (resisitive loads, ACs, Fridges) don't benefit much from switching to DC.

With high voltage DC safety becomes another concern, with arcing being a huge issue.