Prepare the yellow cake mix according to the directions on the box, EXCEPT substitute the can of mandarin oranges (with juice) for the water. Beat the mandarin oranges in with the other ingredients with an electric hand mixer. Bake according to directions.
To make the topping, stir together canned crushed pineapple (with juice), thawed whipped topping, and vanilla pudding mix. Spread over cake evenly once the cake has cooled.