There's no documentation on the Powerdrain Beam in-game or out of game, so I did some testing with a friend. I would shoot their ship with a certain number of linked beams, and they would say whether their power was draining. The ships in question contained mostly power generators. We noticed that sometimes when I fired on the White or Gray hardened hull blocks, the power would not drain, while if I fired on the White Hardened Hull Wedges, it would. We concluded that either the wedges are being considered power blocks, for the 5x effectiveness bonus, or the wedges are not blocking the beam's shot, and allowing it to pass through and hit the power generator blocks.