The simple answer is this; to technically answer you question, every power chord is in a diatonic scale except the one where the scale has a flat 5 (so F# in the key of G major)
The real answer is that that answer is completely useless. Why?
- There are plenty of situations where chords outside of this set also work
Bb and F power chords are both pretty common in rock songs in G major for example.
- In order to know which chords you want to use, you need to have an idea of how each chord behaves, what it can lead to, how it functions in a song etc. If you pick random power chords from the scale (say, |D|E|C|F|A|) it'll probably sound like exactly that, random chords.
That is to say, sometimes chords that are "in a scale" sound bad, and sometimes chords outside of the scale sound great.
Now, maybe your next question would be, "if the major scale is useless in telling me what power chords to use to write a song, what should I use?" The problem is that any list of "rules" of what power chords work well in rock music is pretty much asking "what is the harmonic structure of power chord based music (grunge and punk rock etc.)". That's an interesting question for sure, but requires a very long answer.
It might seem like I'm being obtuse, and or lecturing rather than answering your question, but if you start trying to build rock music from power chords based on the major scale, that's probably worse than basing it on no theory at all. The modern problem of the internet musician is that they often jump straight into "scales" thinking that will teach them how to write music or play solos, when they would learn a whole lot more from the old fashioned way of actually studying pieces of music.
I hope you don't consider this too off-topic from your question, but these are your options:
- Find some books, blogs etc. that go into detailed theoretical analysis about harmony in rock music.
- Listen to, and learn a whole bunch of songs, and try and notice what's going on, what chords get used and when, and why.
- Write "by ear": play what sounds good to you, try and learn from your own intuition.
All to often aspiring songwriters seem to rank them in that order, when
in reality, the musical journey goes exactly the other way round. Hell, I personally love reading about and discussing theory, and always advocate it; but there are plenty of amazing songwriters using just their ears and knowledge of other music. There isn't a single one who learn a couple of scales and tried to piece them together in songs, and didn't bother with the other 2 steps though.