Preheat oven to 350 degrees F.
Grease and flour 13x9-inch pan.
In a small bowl, blend sugar, margarine, milk, vanilla, cream cheese and flour until smooth and creamy; mix in eggs until completely incorporated.
In a large bowl, blend cake mix, water, oil and 3 eggs until moistened; blend at a higher speed for 2 minutes.
Pour half the batter in the greased cake pan; pour filling over batter, and then pour the remaining cake batter over top. Use a knife to make swirls in the batter.
Bake for 30-40 minutes or until toothpick comes out clean.
Allow the cake to cool completely before adding the can of chocolate frosting to the top of the cake.