Fig. 1. 'Don Draper' (John Hamm) - Mad Men
Power and agency are synonymous, but they are not isomorphic. At its worst, power is an end in itself, with the means to match; while agency, when it is predominantly benign, can never be utterly self-serving. Of course, agency without power, or power without agency, are rare. In order to set the two apart, we need to locate them within the matrix of human desire: agency is what we crave, power is what seduces us.
Addendum:
Nirvana -The Man Who Sold The World (click to watch music video)