> What if breaker boxes were "smart" and able to negotiate higher voltages like USB-C does?
That'd be difficult; a breaker typically feeds an entire room, not a single outlet. (And when it does feed a single outlet, that's typically because it's dedicated to a specific large appliance, like an air conditioner or electric stove, which wouldn't benefit from being able to dynamically negotiate a voltage.)
Appliances, like electric range, that need higher power have dedicated 240V circuits. My understanding is that 240V circuits use thicker cable because they usually also have higher current. But it is possible to convert 120V to 240V if only one device, sometimes done for imported electric kettles.
That'd be difficult; a breaker typically feeds an entire room, not a single outlet. (And when it does feed a single outlet, that's typically because it's dedicated to a specific large appliance, like an air conditioner or electric stove, which wouldn't benefit from being able to dynamically negotiate a voltage.)