A power chord is just a 5^th note interval, just the root note and a 5^th note. Typically, played on the heaviest strings. A power chord is neither major nor minor. For power chords, your index finger is always the root note. The great thing about power chords is they are completely portable.

You can also add octaves to make them sound heavier like below.

You can also add a 2^nd octave as well. Basically, making a G5 chord twice. Sounds very heavy.

Other interesting shapes are below.

Don’t forget the good ol’ boogie-woogie below.