Hell no. The only melodic power metal band I know that uses something that resembles death metal is "Burn in Hell". Maybe the song "When Demons Awake" by Rhapsody (now Rhapsody of Fire) can have an approach towards black/death metal, or some Dragonforce songs have growls as well.
Anyways, comparing power metal to death metal is like wanting water to mix with oil, IMO.
Now, Gwar is a bit far, IMO as well. Their songs can have something of death metal, but are far from "happy" songs as well.