Begin by lining a baking sheet with parchment paper or wax paper to prevent sticking and make for easy cleanup.
In a microwave-safe bowl, combine the semi-sweet chocolate chips and creamy peanut butter. Microwave on high for 30 seconds, stir, then microwave in 15-second intervals until fully melted and smooth.
Stir in the vanilla extract, mixing until combined.
In a large mixing bowl, add the Rice Chex cereal. Pour the melted chocolate-peanut butter mixture over the cereal. Gently fold the mixture together using a rubber spatula or wooden spoon until all the cereal is coated.
Sprinkle the cocoa powder over the coated cereal and fold again until the cereal is evenly coated with cocoa.
Transfer the mixture to a large resealable plastic bag. Add the powdered sugar, seal the bag, and shake gently until the mixture is well-coated with powdered sugar.
Spread the coated puppy chow onto the lined baking sheet. If desired, sprinkle mini chocolate chips on top while still warm for added indulgence.
Allow the puppy chow to cool completely at room temperature before serving.