The word "victory" is an abstract noun that can be translated as a verb or an adjective. Alternate translation: "for me to allow you to defeat the Midianites" or "for me to cause you to be victorious over the Midianites" (See: [[rc://en/ta/man/translate/figs-abstractnouns]])
Here "power" represents the people themselves. Alternate translation: "We have saved ourselves without God's help" (See: [[rc://en/ta/man/translate/figs-metonymy]])