In a large bowl combine peanut butter, butter, and sugars. Beat until creamy. Beat in eggs and vanilla. In a small bowl, combine flour, baking powder and salt. Blend into peanut butter mixture. Spread into a greased 9x13 pan. Sprinkle the top with chocolate chips. Place in 350 degree oven for 5 min. Remove from oven and run knife through to marbleize. Return to oven for another 20-25 min.