Sexyback

The song doesn't use power chords but if you are playing it on guitar it sounds better  
just playing the root notes. Basically it's 
 
Verse and Bridge: 
 
A A# A A# A A A A# A 
 
You can figure out the rhythm. 
 
The Chorus is 
 
A Ab A A# A Ab A repeated  
over again 
 
That's pretty much it for the chords.