Power chords can be categorized by the string their root note appears on, thus E5 is described as a root 6 chord because it’s root note is the open 6th string. A5 is a root 5 chord because its root note is the open 5th string, while D5 is a root 4 chord because its root note is the open 4th string.
By using the first finger at the 1st fret and the third finger at the 3rd fret, it is possible to create moveable power chords. This means they can be moved along the strings to create many different power chords. The transition from open power chords to moveable power chords is shown in the diagrams below. The root 5 moveable chord below is called A#5 or Bb5 as it is a semitone (one fret) higher than A and a semitone lower than B.
E5
F5
A5
A#5 or Bb5
Here is an exercise for changing between open and moveable power chords. The open chords are played here with the open string and 2nd finger,