Power chords come in two varieties:
Open-position: The following figure shows the most common open-position power chords — E5, A5, and D5. These chords are merely the two or three lowest notes of the simple open-position E, A, and D chords.
Movable: Movable power chords are simply the two or three lowest notes of the movable barre chords. Movable power chords are either E-based or A-based. The following figure shows the F5 and Bb5 power chords that you play at the first fret, but you can move these chords to any fret.
For the most part, the two- and three-string power chords are interchangeable. Although for some situations, such as playing in the Chuck Berry style, the two-string version is preferable.In rock music (and even in some pop music), guitarists often substitute power chords for full chords to enable the vocal part to stand out more from the music. You can hear this kind of power chord sound in old songs such as “Johnny B. Goode” and “Peggy Sue.” The following figure shows the power chords that you use to produce this kind of sound. Play this progression by using either two- or three-string power chords.
The > symbol is called an accent. It tells you to play those notes a little louder than the others. This forms a rhythmic pattern that gives a song a certain flavor, such as a Latin flavor, a Bo Diddley flavor, a polka flavor, or even a tutti-frutti flavor.
Hard-rock and heavy-metal guitarists use power chords with distortion to create a heavy or ominous sound. They achieve this mood by playing low notes with distortion. The distorted tone they use really limits them to power chords, because full chords (chords with more than two different notes in them) can sound like mud with heavy distortion.
The following figure illustrates a typical heavy-metal riff using both movable and open-position power chords. If you have an electric guitar and an amp or effect device that enables you to overdrive it, use distortion while practicing this progression. You can use either the two- or three-string version of the power chords.