Most powerful music in movies or games.

Samuel Barber - Adagio For Strings
https://www.youtube.com/watch?v=ECQeLQURNuw

in the film platoon

Not a movie. Or a game. But a blast from the past (1978) that will play in your head:
https://en.wikipedia.org/wiki/Jeff_Wayne%27s_Musical_Version_of_The_War_of_the_Worlds
Richard Burton's iconic voice and that soundtrack 👌
Oh, there's a Stage musical production vid on yt:
https://www.youtube.com/watch?v=i6ckXQoBw2M
If you don't know it, at least listen to about the 5 minute mark.

Edit: German version with Curd Jürgens, another iconic, albeit german voice.
https://www.discogs.com/Jeff-Wayne-Jeff-Waynes-Musik-Version-Von-Der-Krieg-Der-Welten/release/12632637

Syd Matters - Obstacles

I'm also going with Endgame, and I also really like The Real Hero, but the music that gives me the most shivers is Portals.
It's such a refreshing take on the Avengers theme, while still staying true to the original.
Plus the scene in itself was highly memorable.
Went to see the movie 7 times in theatres within the 3 first weeks of release, guess that makes me a bit crazy ^^.

the ending scene of Kimi no na wa
i have to hold back tears everytime
https://youtu.be/M40SBBsSCIA

when i do something devious i like to whistle that kill bill diddy

https://www.youtube.com/watch?v=3v9BPxHBogs

Halo OST - Original Halo Theme
https://www.youtube.com/watch?v=xufR_zt9o10

Halo 2 Soundtrack - Blow Me Away
https://www.youtube.com/watch?v=svdR8_w1N0Y

"No Place for a Hero" - Batman: Arkham City
https://www.youtube.com/watch?v=FCTdm8Nb7Ps

Total Overdose Sound Track-Return of the Tres
https://www.youtube.com/watch?v=jaNt113qS5w

Megadeth - Duke Nukem Theme
https://www.youtube.com/watch?v=46MALEk-7cE

Music from Serious Sam, World of Warcraft, DOOM, Lord of the Rings, the catchy soundtrack from Avengers Endgame, Wonder Woman's movie soundtrack, there are plenty more I am sure I am not thinking of right now.

Oldie but still pretty much unbeatable as power themes goes
https://www.youtube.com/watch?v=0JNlOTccdck

well, maybe...
https://www.youtube.com/watch?v=xlYCxbBZUCY

Sunshine - Adagio in D minor
https://www.youtube.com/watch?v=-kSe5tTMOsE

Gladiator - Honor Him
https://www.youtube.com/watch?v=SjwVrEMjyxY

Dragonheart - To the stars
https://www.youtube.com/watch?v=RTlY8lXZaE0

I'm with mdpeters, and:

The Opera scene in Philadelphia:
https://www.youtube.com/watch?v=DwRHwKZSu-w

Por Una Cabeza from Scent of a woman:
https://youtu.be/SwHymXLfgVs

The music for The Fountain, like:
https://www.youtube.com/watch?v=C69RtZzKsFE

The Leftovers - Departure by Max Richter.

https://www.youtube.com/watch?v=iHrKoE1cdEo

https://www.youtube.com/watch?v=rQXigiVjiMQ
Ink (The Complete Soundtrack) - 19. John's Walk

Castlevania: Lords of Shadow 2 Story Trailer
https://www.youtube.com/watch?v=2pMDbF8_uFo

This one has stayed with me over the years. Aleste 2 - Title Theme

Hans Zimmer - Time (Inception - Live in Prague)

https://www.youtube.com/watch?v=OtQX1zQs7jA

The intro song is good as well but for me this song represents that game a lot more despite not being actually part of the game.

Here's the intro in case the first video didn't fill your nostalgia quota.

Does anyone remember this

https://youtu.be/YL-h41b1ADQ

My favourites:
Tron: Legacy, songs "Derezzed" and "Fall" by Daft Punk

Resident Evil Theme by Marilyn Manson

The Dark Knight Rises by Hans Zimmer

The Batman Theme by Danny Elfman

Eye Of The Tiger FTW