_{Mod note:}
Bow enchantet with Power III and Power II resp. Power I and Power I at the same time.

While playing in my survival world after a thunderstorm I was killing some Skeleton Traps and noticed on one of the bows dropped it was enchanted with Power 3, Power 2, and Unbreaking 2. I thought at first it said Punch 2 as one of the skeletons was knocking me back pretty far but then noticed it wasn't punch and that the bow had somehow been enchanted twice. I was able to recreate it by just spawning in more traps and using a looting 3 with Luck effect (if that does anything) with a high strength effect also so always one shot.

To recreate you can also give yourself a looting 100 sword. Although you will get a ton of bones and arrows you will be guaranteed to get a drop of armor and bow.

Code analysis by marcono1234 can be found in this comment.