k - a beginning of an answer:
marxists obviously are materialists, and believe that power comes from people who create our world materially--the workers. and that power is a finite object that some people have and some don't.
classical anarchists split their focus between material bases of power with that of psychological? social/cultural ones? anyway the idea that we are mind as well as body. but classical anarchists seem to agree that power is finite (and, of course, bad).
modern anarchists have adopted Foucault's understanding of power as something that we all have, something that is fluid and moves between us depending on context and personality. That is the main way that modern anarchist thought differs from classical, i would say, and/but the implications are deep (ie we are part of our own oppression and cannot therefore be trusted with creating a new world). feminist anarchists, green anarchists, some APOC, etc, target a specific piece of the current situation as being the crux of the problem--which i would argue speaks to where they find their power base (either personally or socially).
that's as much as i have at the moment.