Preheat your oven to 350°F (175°C) and grease a 9x13-inch baking pan.In a large bowl, combine cake mix, oil, eggs, 1 cup of Dr. Pepper, and chocolate pudding.
In a large mixing bowl or stand mixer bowl, add powdered sugar and give it a whisk to smooth out any lumps. Pour the saucepan mixture over the powdered sugar and mix until well blended.