3 ways depending on the accent, all are acceptable:
1) with a shwa : " fi-uh" ' pow-uh" (Britain, Austrailia, New Zealand, US-- Southern and certain cities - Think James Earl Jones... "You can't resist the pow-uh of the dark side.")
2) " faah" "paah" (Britain, Austrailia, New Zealand, US -- New England and Southern)
3) pronounced hard : " fi-er" "pow-er" (England --- West , Wales, Ireland, US --Midwest, West)