Preheat oven to 350degrees. Sift ½ c sugar, flour and salt into medium bowl 5 times. Using electric mixer, beat egg whites in large (at least 4-quart) bowl until foamy. Add 2 teaspoons warm water and cream of tartar and beat until soft peaks form. Gradually add remaining 1 c sugar and vanilla and beat until stiff but not dry. Sift sugar-flour mixture over whites ¼ cup at a time and gently fold in.
Transfer batter to ungreased 12-cup angel food cake pan with removable bottom. (Do not use nonstick pan.)
Bake until cake is light golden, top springs back when touched lightly and cake begins to pull away from sides of pan (about 45 minutes). Remove cake from oven. Turn cake pan upside down; place center tube of pan over narrow bottle neck or funnel. Cook cake completely.
Using knife, cut around sides and center tube of pan to loosen cake. Push up cake. Cut cake from bottom of pan. Transfer to platter. (Can be made 1 day ahead. Wrap tightly with plastic and store at room temp.)
Dust cake with powdered sugar. Garnish with crystallized ginger, if desired. Serve with Mango-Ginger sauce.