Measure out the Chex cereal into a large bowl and set aside.
In a microwave safe bowl, microwave the chocolate chips, peanut butter, and butter on high for about 30 seconds. Give the mix a stir. Continue to microwave and stir in 15 second intervals until the mixture is melted and smooth. You can also melt these ingredients by placing them in a heat safe bowl over simmering water. Stir frequently until the mixture is completely melted and smooth.
Once the chocolate peanut butter mixture is melted, stir in the vanilla.
Pour the chocolate over the Chex cereal and gently toss until thoroughly coated.
Transfer the chocolate covered cereal to a large freezer bag or large bowl and add the powdered sugar. If using a bowl, make sure to cover it!
Shake the mixture until the cereal is completely coated in the powdered sugar. At this point you can either leave it in the large bowl, or move it to a sheet pan or large baking dish.