@Stefan: When you're using nouveau.runpm=-1, nouveau is always used to dynamically power down the card. This works because a Dell XPS 9550 ships with a GeForce GTX 960M, which nouveau is actually able to power down, unlike the more recent XPS 560 with a GTX 1050.
@Stefan: When you're using nouveau.runpm=-1, nouveau is always used to dynamically power down the card. This works because a Dell XPS 9550 ships with a GeForce GTX 960M, which nouveau is actually able to power down, unlike the more recent XPS 560 with a GTX 1050.