Heat oven to 375°F. Line 15-1/2x10-1/2x1-inch jelly-roll pan with foil; generously grease foil. Sprinkle linen or thin cotton towel with 1/4 cup powdered sugar.
Beat egg whites in large bowl until soft peaks form; gradually add 1/2 cup granulated sugar, beating until stiff peaks form.
Beat egg yolks and vanilla in medium bowl on medium speed of mixer 3 minutes. Gradually add remaining 1/3 cup granulated sugar; continue beating 2 additional minutes.
Stir together flour, cocoa, baking powder, baking soda, and salt;
add to egg yolk mixture alternately with water, beating on low speed just until batter is smooth.
Gradually fold chocolate mixture into beaten egg whites until well blended.
Spread batter evenly in prepared pan.
Bake 12 to 15 minutes or until top springs back when touched lightly in center. Immediately loosen cake from edges of pan; invert onto prepared towel. Carefully peel off foil.
Immediately roll cake and towel together starting from narrow end; place on a wire rack to cool completely.