I had passing interest in the Darpa exoskeleton stuff quite some time ago. Kazerooni is well known in his field. I might have even met him. I think the one that won the first design competition had a gas engine powered unit/backpack and was hydraulic. One of the guys was Jacobsen who went on to design an electric wraptor-like rope ascender. Bit complicated and boxy, not sure of it's commercial end. His original tech Schtick was a micro turbine geared down, tried to run on combustion gases. Not sure how that eventually turned out. I think the other (more famous) Jacobsen was the main competition in force feedback robotics. 80's, 90's work maybe these guys are starting to retire. I think one of them was doing Disney animatronics etc.
very interesting stuff. for fun look up the robotic dogs and walking variations. very similar research.