For the Cheddar popcorn: Melt the butter in a large heavy-bottomed pot over medium-high heat. Remove from the heat and fold in the popcorn to coat. Sprinkle in the cheese powder and mustard powder. Fold together to evenly coat. Transfer to a large serving bowl.
For the caramel popcorn: Preheat the oven to 300 degrees F. Line a baking sheet with foil and generously spray with nonstick spray.
Wipe the large pot clean of any excess popcorn residue. Add the brown sugar, corn syrup and butter to the same pot and bring to a boil over medium-high heat, stirring constantly, about 3 minutes. Reduce the heat to medium and continue to let it boil, without stirring, until it turns a deep golden brown, 4 to 5 minutes.
Remove from the heat and stir in the salt, vanilla and baking soda. Gently fold in the popcorn until well coated (spraying a rubber spatula works well, here!). Transfer the popcorn to the prepared baking sheet and bake until the caramel has melted around the popcorn and nicely coats the kernels all over, about 10 minutes. Let cool completely on the baking sheet, about 10 minutes. Break into pieces and add to the serving bowl.