To make the buffalo sauce, add 1/3 cup hot sauce, 3 tablespoons butter, 1 tablespoon white vinegar, 1 teaspoon Worcestershire sauce, 1/2 teaspoon cayenne, and 1 teaspoon garlic powder to a medium bowl. Mix well to combine.
Add the cooked, shredded 2 cups boneless skinless chicken breasts to the bowl of sauce, then toss to coat evenly. Set aside.
Add 16 ounces elbow macaroni to a large pot and cook following the package instructions. Drain and rinse the cooked macaroni, then set aside.
In a large pot, add 1/3 cup butter over medium heat. When the butter is melted, add in 1/3 cup all-purpose flour and whisk to combine.
Slowly pour 2 ½ cups whole milk into the butter mixture, whisking continuously to prevent lumps from forming.
Add the shredded 2 cups Monterey jack cheese, 1 ½ cups cheddar cheese, 1/2 cup hot sauce, and salt and pepper to taste. Stir continuously to melt the cheese.
Once the cheese has melted, remove the pot from the heat then stir in the cooked macaroni. Stir well to evenly coat the noodles.
Gently stir in the buffalo chicken until fully incorporated.
Garnish with additional sauce and sliced green onions. Serve warm and enjoy!