It's strange how many people get lost in the difference between power chords and bar chords.
For those people I will start off by saying power chords have 3 fingers on 3 strings and bar chords have 1 finger on ALL strings and chords using you pinky, ring and middle finger.
Let's go onto a power chord called F5.
That is a power chord, I will now show you a bar chord called F
Power chords are known to be used in rock music like; Nirvana
, Foo Fighters
, Pearl Jam
You can still use bar chords in rock music just power chords give a 3 note sound.
Hoped I helped,