Lee DeWyze -- The Marilyn Manson Phase

Back before he won "American Idol" -- Lee DeWyze flirted with the dark side ... in fact, dude covered a song by Marilyn Manson.

DeWyze's old record label has just released Lee's rendition of Manson's hit "Beautiful People" -- roughly one year after Lee recorded it back in Chicago.

While the cover ain't half bad -- we're told the song never made the cut on any of Lee's old albums.