On medium low heat melt the butter, chocolate chips and SunButter together until smooth and completely melted through. Remove immediately, add in vanilla and mix well. Pour over Chex cereal and fold cereal with melted SunButter mixture until all the cereal is well coated. In a gallon sized bag, add powdered sugar. Place a couple cups of cereal mixture at a time into the ziplock bag, seal and shake. Continue until all cereal has been added to powdered sugar and shaken to cover well. Store at room temperature or in the fridge for 3-5 days in an airtight container.