Root on A string
x244xx
B5 is the B power chord. Its notes are B and F♯. No third means no major or minor quality. Mute unused strings carefully.
x244xx
799xxx
Numbers show frets from the low E string to the high e string; x means don't play that string.
Every B and F♯ on the first 12 frets. The filled dots are the root, B. Build your own shape from any nearby group.
Other B chords
Other power chords