Beat the yellow cake mix, peanut butter and brown sugar unless it becomes flaky. (Low speed)
Separate ½ cup from mixture.
To the rest of the beat mixture, add water, eggs and oil and blend until moistened. (Low speed)
On a higher speed beat further 2 minutes.
Add ¼ cup of peanut butter chips and ¼ cup of chocolate chips. Stir.
Take a greased baking pan of size: 13x9x2 inches. Pour in the mixture.
Mix together the separated ½ cup of mixture, peanuts and chips.
Sprinkle on top of the mixture in the pan.
At 350 degrees, bake for 40-45 minutes.
To check, insert a toothpick. Cake remains uncooked unless toothpick comes out clean.