Line a baking tray with parchment paper to prevent sticking and set aside.
In a microwave-safe bowl, combine the semi-sweet chocolate chips and creamy peanut butter. Microwave in 30-second intervals, stirring between each, until melted and smooth.
Once melted, stir in the cocoa powder and vanilla extract until well combined.
In a large mixing bowl, add the Rice Chex cereal. Pour the melted chocolate mixture over the cereal and gently fold to coat all the pieces evenly.
Once the cereal is fully coated, transfer it to the prepared baking tray and spread it out in an even layer to cool for about 10 minutes.
After cooling, place the puppy chow in a large zip-top bag. Add the powdered sugar and shake gently until the mixture is well coated.
If desired, add mini chocolate chips to the puppy chow and give it a final gentle mix, ensuring they stick to the mixture.
Allow the puppy chow to cool completely before serving. Store in an airtight container for up to one week.