Brown ground beef and onion together in a large skillet over medium heat; drain. Stir in soup and chili powder. Spread in an ungreased 13"x9" baking pan; top with corn chips. Bake, uncovered, at 350 degrees for 20 to 25 minutes. Remove from oven; sprinkle with cheese. Bake for an additional 5 minutes, until cheese melts.