Preheat the oven to 400°F (200°C). Lightly grease a 9×13-inch baking dish.
Wash the potatoes and cut them into evenly sized bite-sized pieces.
Add the potatoes to a large bowl. Pour in the melted butter and add the garlic powder, onion powder, smoked paprika, salt, and black pepper. Toss until evenly coated.
Add the ranch dressing and toss again until the potatoes are well coated.
Stir in half of the cheddar and Monterey Jack cheese, reserving the rest for the topping.
Transfer the potatoes to the prepared baking dish and spread them into an even layer.
Cover loosely with foil and bake for 30 minutes.
Remove the foil and sprinkle the remaining cheese evenly over the potatoes.
Bake uncovered for another 15–20 minutes, or until the potatoes are fork-tender and the cheese is melted, bubbly, and lightly golden.
Let the potatoes rest for a few minutes, then garnish with chopped parsley or green onions.
Serve warm with your favorite main dish.