If what you mean is the sound of electric guitar doing power chords... I just use an old Roland module. What I've found is that it sucks unless I put it through a tube amp and mic it.
Also, for that sort of thing you can't play "normal" piano type, stacked thirds chords. I usually play stuff like 1 and 5 with no thirds. The harmonics will add the third. There's lots of distance between the notes in guitar chords compared to piano chords.
It's more the chords you play and what you play it back through, the source sound doesn't matter as much as the rest I don't think, the same as real guitar.