Heat-treat the cake mix: Place the funfetti cake mix in a microwave-safe bowl and microwave in 30-second increments, stirring between each, until the temperature of the mix reaches 165°F on an instant-read thermometer (this should take about 90-120 seconds). Set the cake mix aside to allow to cool. *
Add Chex cereal to a large mixing bowl and set aside.
Place the candy melts in a microwave-safe bowl. Microwave in 30-second intervals, stirring after each, until they are smooth and completely melted.
Pour the melted candy over cereal and stir gently to coat.
Add the sprinkles in by the Tablespoon, gently stirring the whole time. Do not overmix or it can cause the sprinkles to melt.
Add the cake mix and powdered sugar to a gallon-size zip-top baggie. Seal the bag and give it a shake to combine.
Open the bag, add half of the candy-coated cereal, close the bag, and gently shake to coat the cereal. It is ready when the cereal is coated and is no longer sticky. If the cereal is not coated enough, add more powdered sugar by the Tablespoonful. Once you are done with the first half of the Chex, repeat the process with the second half.
Pour the puppy chow out onto wax or parchment paper. Allow it to set and cool completely before storing or serving.
Notes
Store in an air-tight container at room temperature for up to one week or in the fridge for up to two weeks.If you don't have candy melts, you can use white chocolate chips or almond bark.* Although it is rare, the uncooked flour in the cake mix could be contaminated with bacteria that cause food-borne illness. That is why it is best to play it safe and heat-treat the cake mix before using it.