The Dark Powers are powers possessed by evil characters in Tolkien's legendarium. These are powers of corruption wielded by Melkor and Sauron in the forms of the Discord Of Melkor and the Rings of Power. It seems that the all encompassing darkness is one capability alongside necromancy.
Known wielders of the Dark Powers are Sauron, Ungoliant, the Witch-king of Angmar, and Melkor.