I'm not sure I understand your question correctly but a powerchord is a root and a fifth.

So if you are to play the A5 powerchord, you'll have to play the 5th fret on the 6th string and the 7th fret on the 5th string.

The A (5th fret 6th string) is your root note
The E (7th fret 5th string) is your fifth note

Powerchords are always the same, a root and a fifith.

So if you were to play a A5 powerchord on the 4th string you would have to play the A (7th fret 4th string) and the E (9th fret 3rd string).