Preheat oven to 350 degrees F. Lightly grease 12-cup fluted tube pan or 10-inch tube pan; set aside.
Beat all ingredients except chopped chocolate in large bowl with electric mixer on low speed just until moistened, stopping frequently to scrape side of bowl. Beat on medium speed 2 min. or until well blended. Stir in chopped chocolate. Spoon into prepared pan.
Bake 50 min. to 1 hour or until toothpick inserted near center comes out clean. Cool in pan 10 min. Loosen cake from side of pan with metal spatula or knife. Invert cake onto wire rack; gently remove pan. Cool completely. Sprinkle with powdered sugar just before serving.