This “higher input voltage is more efficient” can also happen with bridge/protection diodes. (E.g. devices that accept AC or DC, or any polarity of DC, or at least safely refuse to function if you plug in a barrel connector with the wrong polarity)

They’ll cause a fixed voltage drop, so the higher the voltage you put in, the lower the proportion of your power you lose.

240V computer power supplies are a bit more efficient than 120V ones because of this.