I'd say more heavy metal than power metal in terms of his vocal styling. I mean, he's been in Masterplan and Avantasia, who are power metal (and Masterplan's "Time to Be King" and then the other albums - make sure he's actually the vocalist on them though, because IIRC they've had three different singers - would probably be where I'd suggest to start) , but the way he sings is very reminiscent of David Coverdale and Dio.
For pure vocal performance, I'd look to Beyond Twilight's "The Devil's Hall of Fame" and Ark's "Burn the Sun" albums. For the first album, the song Crying is a great example of what he can do (once you're past the weird humming at the start),
and then Missing You from the Ark album.
and just as an additional extra, the song where I first "found" him, Avantasia's "The Scarecrow" (Tobi Sammett and Michael Kiske are also on this one). I think big projects like Avantasia, Ayreon (Jorn's also on one of their albums) and so on are great ways to discover new singers, actually. Nothing to do with what we're talking about here, just thought I'd add that in.
His solo stuff is more straight up hard rock, and rather irritatingly that's where he seems to be happy to stay for the time being. I like it, but I tend to prefer him in a band because when he's working as part of a group he seems to stretch his vocals more.