In a large bowl, measure out the Chex cereal and set aside.
In a microwave-safe bowl, combine the peanut butter, butter, and white chocolate chips. Microwave in 30-second intervals, stirring between each, until the mixture is smooth and fully melted.
Add the pumpkin puree, pumpkin pie spice, and vanilla extract to the melted mixture. Stir until well combined.
Pour the pumpkin mixture over the Chex cereal and gently stir until all the cereal is coated.
Add the powdered sugar to a large zip-top bag.
Working in batches, add some of the coated cereal to the bag with powdered sugar. Seal the bag and shake gently until the cereal is coated with sugar.
Spread the coated cereal on a baking sheet lined with wax paper to cool and set.