Heat oven to 325°F. Grease 12-cup fluted tube cake pan with shortening (do not use cooking spray); coat with flour. In large bowl, beat sugars and butter with electric mixer on low speed until well blended. Add milk, vanilla and eggs. Beat on medium speed 2 minutes.
Beat in flour, baking powder and salt until mixture is smooth and well blended. Spread in pan.
Bake 1 hour 5 minutes to 1 hour 15 minutes or until toothpick inserted in center comes out clean. Cool 10 minutes. Remove from pan. Cool completely, about 2 hours.
In 1-quart saucepan, heat caramel topping and rum over low heat, stirring occasionally, until well blended and warm. Serve warm topping over slices of cake.