In a large microwave-safe bowl, combine chocolate chips, peanut butter, and butter. Microwave in 30-second intervals until melted and smooth, stirring in between.
Stir in vanilla extract until well combined.
Pour Chex cereal into the chocolate mixture and gently stir until all pieces are evenly coated.
Transfer the coated cereal into a large resealable plastic bag. Add powdered sugar, seal the bag, and shake until all the cereal is coated with powdered sugar.
Spread the puppy chow onto a baking sheet to cool and set.
Once cooled, transfer to a serving bowl and enjoy!