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Tony just hinted at it, a power chord is typically just a 2 or 3 string chord. You make pretty much the same shape as the C# minor, but you don’t have to flatten your index finger or place the middle finger. So you’re only holding down the A string with your index finger (making a C# on fret 4) then you use ring and pinky on the 6th fret D and G strings (making G# and C#).
Adopt the same concept for the G bar chord. Instead on the A string you are holding down the low E string on the third fret to make a G, and place ring and pinky on the 5th fret.
These are 3 string chords, so you are only playing A, D and G strings for C#m power chord, and E, A and D strings for the G power chord.
Edit: finished listening all the way through and then realized Tony runs through the power chords starting at about the 10:15 mark of the Learn video. You can hardly hear the difference between them and the bar chords – wow, amazing when you have Tony’s playing skills!