Preheat your oven to 350°F (175°C). Grease and flour a 9×13-inch baking pan.

In a large mixing bowl, whisk together the flour, cocoa powder, sugar, baking soda, and salt until well combined.

Add the Dr Pepper, eggs, vegetable oil, and vanilla extract to the dry ingredients. Mix gently until just combined; avoid overmixing.

Pour the batter into the prepared pan evenly. Bake for 30-35 minutes or until a toothpick inserted comes out clean.

Allow the cake to cool in the pan for about 10 minutes before transferring it to a wire rack. Dust with powdered sugar before serving.