I alternate pick non palm muted power chords a lot, especially when getting a more complicated rythym going. I sometimes mix downstrokes with alternate picking.

I played mandolin for many years and developed alternate picking over double strings a long time ago, of course this is a little different than alternate picking power chords, but the method is the same.

It takes me practice to get an even down and up stroke going that is balanced and good sounding. A soft pick hand definitely helps and not digging in also is important for me. It may be that heavy duty players like SRV or Kenny Wayne Shepherd could/can dig in and alternate pick power chords with no problem. I wouldn't doubt that the same is true for many other expert players.

I would guess that you can alternate pick power chords with increasing accuracy and good results with lots of practice, starting with a soft hand and not digging in too deep.

Just watched Kenny Wayne Shepherd on Direct TV Sessions and he does some serious guitar playing, one of his inspirations being SRV and a lot of the old blues greats. In fact he mentions that when he was 13 a fairly big blues star let him sit in on stage for his first stage performance and that he played with a lot of semi famous and famous blues players, including some of the surviving members of some of the greatest old school American blues players. A great performance if you can still catch it on channel 101 on Direct TV. It was really fun watching him play, you can really see his influences coming thru. "Blue on Black" is really a cool song.

My first guitar teacher, that I eventually fired, never even taught me any alternate picking. My next teacher said he couldn't have been much of a teacher. Since then I have been working on my alternate picking whenever I can and it definitely saves energy.