I am learning to play extended power chords and one issue I am facing is buzz when playing these chords down the neck on frets 10 and above. Should I make any changes to the fingering of my ring finger and pinky? I am sure it's the fingering of ring finger and pinky.
Make sure that your fingers are centered on only one string each and practice the chord a lot. Your finger might be touching one of the frets, which could cause the buzzing sound.
Almost anything can be refingered, if you're having trouble consider moving it. eg, from 10th fret low E to 5th fret A.
Buzz is usually a sign that you're guitar is improperly setup - do the notes buzz when you fret them as single notes? If so, get a setup with a local tech.