Stir the soup and sour cream in a small bowl.
Heat the butter in a 3-quart saucepan. Add the onion and chili powder and cook until the onion is tender, stirring occasionally. Stir in the turkey, chiles and 2 tablespoons soup mixture.
Spread 1/2 cup soup mixture in a 2-quart shallow baking dish. Spoon about 1/4 cup turkey mixture down the center of each tortilla. Roll up the tortillas and place, seam-side down, into the baking dish. Pour the remaining soup mixture over the filled enchiladas. Sprinkle with the cheese.
Bake at 350°F. for 25 minutes or until the enchiladas are hot and bubbling.