To a microwave safe bowl, add chocolate chips, peanut butter, and butter. Microwave for 30 seconds, and stir well.
Microwave for 30 seconds more, and stir again. If not melted, microwave on 15 second increments and stir until smooth. Remove from the microwave and stir in vanilla extract, mixing well.
Pour the chocolate mixture over the chex cereal, and toss to coat.
Divide the powdered sugar between two gallon storage bags.
Scoop the chocolate covered chex into the gallon bags, and shake well to coat the cereal in the sugar.
Spread the coated cereal onto a parchment lined baking sheet, and allow to set for about 30 minutes.