There are a lot of albums I could include here and in many cases I could have chosen a different album for a given band but in sticking to one album per band here is my list (in alphabetical order).
Blind Guardian - At the Edge of Time
Firewind - Immortals
Noble Beast - Noble Beast
Orden Ogan - To the End
Persuader - Evolution Purgatory
Pyramaze - Disciples of the Sun
Stratovarius - Eternal
Sunburst - Fragments of Creation
Symphony X - Paradise Lost
Unleash the Archers - Apex
Others I considered:
Adagio - Underworld
Almah - Fragile Equality
The Approach and the Execution - Kings Among Runaways
Borealis - Fall from Grace
Brainstorm - Midnight Ghost
Crimson Shadows - Glory on the Battlefield
Diviner - Fallen Empires
Edguy - Hellfire Club
Falconer - Falconer
Fireleaf - Behind the Mask
Gladenfold - From Dusk to Eternity
Guardians of Time - Rage and Fire
Helion Prime - Terror of the Cybernetic Space Monster
Hibria - Defying the Rules
Iced Earth - Burnt Offerings
Immortal Guardian - Age of Revolution
In Vain - The Little Things That Matter
InnerWish - Innerwish
Labÿrinth - Return to Heaven Denied
Lost Horizon - Awakening the World
Paladin - Ascension
Pharaoh - The Longest Night
Project Arcadia - A Time of Changes
Rage - Soundchaser
Reverence - Gods of War
Sacred Outcry - Towers of Gold
Savage Circus - Dreamland Manor
Seven Kingdoms - Decennium
Shadowseer - Shadowseer
Solarus - Reunion
Tanagra - None of this is Real
Theocracy - Mosaic
Triosphere - The Heart of the Matter
Wardrum - Mavericks
Widow - Carved in Stone
List with comments:
Blind Guardian - At the Edge of Time (Could have picked a few different BG records but I go back to this one often. Sacred Worlds is one of my favorite album openers of any genre)
Firewind - Immortals (I've always been a fan of Firewind but they never seemed to put a complete album together until Henning Basse joined the band and they produced this masterpiece)
Noble Beast - Noble Beast (Turns out the vocalist is a shitty human so this will be the only album we ever get from them but it's one of the more unique sounds in power metal. We Burn is fucking awesome)
Orden Ogan - To the End (Their discography is up and down but I return to this one often. The Frozen Few into To the End sets the bar high to start and the quality never really dips. The Ice Kings is probably my favorite ballad in power metal)
Persuader - Evolution Purgatory (A few years ago I probably would have chosen When Eden Burns in this spot but this one has aged better for me. Jens Carlsson sounds phenomenal here)
Pyramaze - Disciples of the Sun (This was one of the most pleasant surprises for me at the time. I always liked elements of their music but they finally found their sound when Terje came on board)
Stratovarius - Eternal (I'm really torn on which of their albums to pick and would probably choose something else tomorrow but their recent run has been elite)
Sunburst - Fragments of Creation (I don't think it's hyperbolic to refer to Gus Drax as the most underrated guitarist on the planet. From a technical perspective, he is insanely clean and his songwriting is also first-rate. His cover of Altitudes is the best I've heard and he's done great work in Black Fate, Suicidal Angels, and in his solo career. Pair that with Vasilis Georgiou's vocals and you have the recipe for one of my favorite albums of all time)
Symphony X - Paradise Lost (Another band with many albums I could have chosen but this is probably the most "power metal" they get)
Unleash the Archers - Apex (I remember first hearing their sophomore album and cringing at their weird attempt at mixing melodeath and power metal. For whatever reason, I gave them another try when Time Stands Still came out and I'm glad I did because they leaned into what they actually do well and then managed to create what should be an all-time classic in the aptly named Apex. Everything here from the vocals to the drumming to the story and songwriting is top notch)
Adagio - Underworld (Similar to Symphony X in that they are more progressive than power metal but David Readman is a monster vocalist and the energy on this album is great)
Almah - Fragile Equality (I'm probably the only person on the planet who prefers Almah to Angra. They got proggier after this album but this is straight up power metal)
The Approach and the Execution - Kings Among Runaways (Their genre is tough to pin down given their thrash/heavy metal influence but this album has a very power metal feel given the focus on melody and energetic choruses)
Borealis - Fall from Grace (I've never understood why this band hasn't been bigger. Their albums have consistently been high quality with an emphasis on melodic and catchy songs)
Brainstorm - Midnight Ghost (Tougher/grittier take on power metal with big choruses)
Crimson Shadows - Glory on the Battlefield (I hesitate to include this given they use predominantly harsh vocals but instrumentally they are basically power metal)
Diviner - Fallen Empires (I could substitute any of their albums here. MA lists them as heavy metal but the riffs and huge choruses feel more power metal to me)
Edguy - Hellfire Club (Edguy's discography is a little all over the place for me but they absolutely nailed it on this one)
Falconer - Falconer (Black Moon Rising may actually be better but I have a lot of nostalgia for this one)
Fireleaf - Behind the Mask (I don't know what happened to this band but this is an album I have forgotten about and then remembered again seemingly every year since it came out. Tough and gritty stuff)
Gladenfold - From Dusk to Eternity (Another band that features a lot of harsh vocals but I would still categorize more as power metal than melodeath. All of their albums are great but Where Fires Burn Frozen gives this one the nod for me)
Guardians of Time - Rage and Fire (This band has all the elements people like in power metal but never seemed to gain much steam. Riffs are a little on the heavier/crunchier side with soaring vocals and huge choruses)
Helion Prime - Terror of the Cybernetic Space Monster (The first album was great too but Sozos Michael's vocals fit this perfectly for me)
Hibria - Defying the Rules (This album is the definition of high flying and in your face power metal)
Iced Earth - Burnt Offerings (One of the few bands here where I don't care for most of their discography but I played the shit out of this when I was first getting into power metal)
Immortal Guardian - Age of Revolution (This band doesn't get enough love. They've got crazy energy and great vocals)
In Vain - The Little Things That Matter (Similar to a band like Desert Near the End in that they have a lot of thrash elements and maybe barely qualify for power metal but this is just such a fun album)
InnerWish - Innerwish (This is a little more mid-paced with very Gus G-like riffs and massive choruses)
Labÿrinth - Return to Heaven Denied (I actually don't care for a lot of the 90s power metal pioneers for whatever reason but this is just such a fun album)
Lost Horizon - Awakening the World (It's such a shame this band only managed to create two albums)
Paladin - Ascension (High energy power metal infused with thrash)
Pharaoh - The Longest Night (It's tough for me to choose between their albums but I tend to return to this most often)
Project Arcadia - A Time of Changes (They have actually managed to make three great albums with three different vocalists but I haven't had enough time with the latest and I'd give A Time of Changes a slight edge to the debut)
Rage - Soundchaser (Rage has a lot of albums to choose from but this is the one that introduced me to them and I probably return to it the most)
Reverence - Gods of War (I guess this is more on the traditional heavy metal/USPM side, Hall sounds great on this record)
Sacred Outcry - Towers of Gold (I haven't spent as much time with this one yet but Daniel Heiman sounds phenomenal here)
Savage Circus - Dreamland Manor (I guess they are like discount Blind Guardian but it's a very small discount)
Seven Kingdoms - Decennium (Fast, upbeat, high energy female-fronted power metal)
Shadowseer - Shadowseer (US band with progressive/thrash/heavy metal elements. I've always wondered what they could have done had they stuck together for another album)
Solarus - Reunion (This band is basically Borealis with a female vocalist)
Tanagra - None of this is Real (One of the more unique bands I've heard. Some of their riffs remind me of the newer retro sounding power/heavy metal bands like Visigoth but there is more of a focus on melody and an emotive sound)
Theocracy - Mosaic (They just have this sound down pat...)
Triosphere - The Heart of the Matter (Another band with a unique sound that mixes elements of prog and heavy/thrash metal with clean and catchy choruses)
Wardrum - Mavericks (I think Awakening may be a better album but this one is more impressive given I basically wrote this band off after Yannis left but the songwriting here is as good as ever and the new vocalist is a worthy replacement)
Widow - Carved in Stone (Another band with seemingly more traditional heavy metal influence than power metal. The riffs and choruses are competing with each other to get stuck in your head)