Although Loudness is more Heavy metal than Power Metal (and has been discussed for quite some time now what they actually are, feel free to move it if it doesn't belong here) , these guys are just plain awesome. True legends actually.
https://www.youtube.com/watch?v=ZRJ4Re8jKWU
https://www.youtube.com/watch?v=KiK7iLEOiXs
https://www.youtube.com/watch?v=-rI1rOwWlYk&feature=related
Enjoy!!