Preheat oven to 350°F and grease a 9×13-inch baking dish.
In a mixing bowl, beat cake mix, eggs, oil and water until well combined. Add one can of mandarin oranges to batter and beat until well blended.
Pour batter into baking dish and bake for 30-35 minutes, or until toothpick inserted in center of cake comes out clean. Allow cake to cool.
For the topping: In a large bowl, stir pudding mix and pineapple. Fold in thawed whipped topping. Frost the cooled cake and top with the second can of mandarin oranges.
Chill for a minimum of 30 minutes before serving.