Grease and flour a 10-inch fluted tube pan. Set aside.
In a large bowl, combine the cake mix, pudding mix, sour cream, water, cooking oil, and eggs. Beat with an electric mixer on low speed for 30 seconds. Beat on medium to high speed for 2 minutes more (the cake batter will be thick).
By hand, stir the semisweet chocolate pieces into the batter. Pour the cake batter into prepared pan.
Bake in a 350 degree F oven about 1 hour or until a toothpick inserted near center of the cake comes out clean.
Cool cake in pan on a wire rack for 15 minutes. Remove cake from pan; cool completely on a wire rack. Sift powdered sugar over the cake. Makes 16 servings.