The villain gets powerful by destroying others as he gains their energy. But eventually the hero defeats the villain. In this movie the fighters get powerful by acquiring energy by destroying others. Does anyone know this movie?

Could be

The One (2001) (http://www.imdb.com/title/tt0267804/)

Actually, now I re-read, sounds more like this one...

Highlander: Endgame (2000) (http://www.imdb.com/title/tt0144964/)