The description is: "Standing power attacks do 25% bonus damage with a chance to decapitate your enemies."

However, my latest character, an Imperial two-hander, never gets decap animations when she does a power attack, standing or otherwise, using her greatsword. They only seem to occur with regular attacks. Have others had the same experience?

Also, I've heard various recommendations to "aim at the head" when attacking if I want a decap. This seems dubious to me. Any truth to it?

Maybe you're just getting unlucky, but I've only got 'Devastating Blow' once, as I prefer one handed.