PREHEAT oven to 375° F. Grease 10-cup Bundt or tube pan.
COMBINE cake mix, eggs, sour cream, vegetable oil and water in a large mixer bowl. Beat on low speed until moistened. Beat on high speed for 2 minutes.
PLACE 1 1/2 cups batter in a medium bowl; stir in Choco Bake. Alternately spoon batters into prepared baking pan, beginning and ending with yellow batter.
BAKE for 35 to 45 minutes or until wooden pick inserted in cake comes out clean. Cool in pan for 20 minutes; invert onto wire rack to cool completely. Dust with powdered sugar before serving.