Power chords are neither major or minor. Power chords, also called 5th chords, contain no third, so, therefore, there is no minor or major tonality.

This means that virtually any scale based on the root of the power chord can be used to solo over that particular chord. Over just a C power chord, you could play C major, minor, dorian, phrygian, etc, and it would all sound fine. Once again, this is because the power chord contains no 3rd.

However, if you're attempting to solo over a progression of power chords, it's the sequence of the chords and their relative positions that determines what scale to play.

I don't know what the other chords in the progression are, but for just C# and G#, you could play almost anything. Any scale that contains all the notes of the G# and C# power chords would work. I would start out in G# minor pentatonic.