[kragen]

No. Carborundum can operate at higher temperatures and voltages than silicon, but it isn't more efficient; it just lets you run the transistors hotter and at higher voltages, so they can switch more power. The nitride is actually more efficient, but it's more delicate to overvoltage. (I think it also withstands higher temperatures, but in a wallwart the problem isn't that the transistor loses its ability to switch; it's that the plastic case melts.)

You can relive my emotions from when I learned about the astounding properties of nitride transistors (in 02017, I think) in https://dercuano.github.io/notes/jellybeans.html#addtoc_1. Unfortunately there weren't any carborundum parts in my list.