Maddolis, I added all of those except Paradise Lost because I wasn't sure whether or not Symphony X is technically a power metal band. If you guys think they are I'll be glad to add a bunch of their albums though.
I also added a bunch of Epica and Within Temptation, and one Alestorm album.
As for a Top 10, how's this?
1. Keeper of the Seven Keys (Parts 1 and 2) - Helloween
2. Battle Hymns - Manowar
3. Land of the Free - Gamma Ray
4. Oceanborn - Nightwish
5. To Mega Therion - Therion
6. Symphony of Enchanted Lands - Rhapsody
7. Epica - Kamelot
8. The Metal Opera - Avantasia
9. Theater of Salvation - Edguy
10. The Dark Saga - Iced Earth
I see your hesitation with Paradise Lost but seeing as it's prog/power (compared to much of their earlier, more neoclassical/prog albums) I figure the power metal influence is fairly high. It's also a lot more power metal than Transcendence (traditional/'prog' though I tend to disagree with the prog label given to Crimson Glory and early Queensryche) and Outworld.
Also I wouldn't put any Avantasia in the top 10, nor Edguy (though they should be higher than Avantasia). There should be at least two Helloween albums in the top 10 before anything by Edguy, Rhapsody or Avantasia. Blind Guardian's Nightfall in Middle Earth should probably make the top 5 as well, edging out Nightwish. Stratovarius should make the top 10 before Avantasia, Edguy and Rhapsody.
Also To Mega Therion is a Celtic Frost album, and I'm fairly hesitant on them making the top 10 too.
Some other (IMO more worthy) suggestions for the top 10 (keep KotSK, Battle Hymns, Land of the Free, The Dark Saga/Burnt Offerings):
Imaginations from the Other Side
Nightfall in Middle Earth
Walls of Jericho
The Black Halo (this or Epica, not sure if I'd have both)
Stratovarius - Visions
Also if you're going to have Alestorm you may want to consider having Wintersun on there. Wouldn't fare quite as highly on a power metal list as it would on melodeath perhaps but just a thought.