Used to express extreme excitement or approval of someone or something. Generally has no connection or relevance to the topic at hand, much like yelling "High ho silver!" amidst a discussion or debate.
This phrase was made famous by the fictional character He-Man from the animated series "He-Man and the Masters of the Universe" (1983-1985), which ran for 130 episodes and was based upon Mattel's popular toy line. During various confrontations in the show He-Man would utter "By the Power of Grayskull...I Have the Power!" which is what popularized this phrase.