Preheat oven to 350F degrees. Spray 12-cup Bundt pan (or 13x9 baking pan) with cooking spray and set aside.
In a medium bowl, whisk flours, granulated sugar, cocoa, baking powder, baking soda, and pumpkin pie spice.
Put buttermilk, pumpkin puree and brown sugar in a large bowl and beat with an electric mixer on low speed. Beat in egg and egg white. Add oil, corn syrup and vanilla and continue beating on low.
Gradually add dry ingredients, stirring until just combined. Fold in chocolate chips.
Pour batter into prepraed pan.
Bake for 1 to 1¼ hours in Bundt pan (or 20 to 25 minutes in 13x9 pan), or until a toothpick inserted in the center comes out clean. Let cool on wire rack for 15 minutes and then remove from pan to cool completely on wire rack. Dust with powdered sugar before serving.