USB PD (Power Delivery) actually does use a higher voltage for more wattage. Standard USB is limited to 5V at 0.5A and sometimes up to 5V @ 2A on quick chargers. But PD chargers can give 20V and 3A for 60w or even 5A (100w) with properly rated cables. There’s even a proposal for up to 48V at 5A to get 240w. This is all determined by a negotiation between the charger, the cable (which does have a small chip for this purpose), and the device, therefore PD chargers must support multiple voltages.