Preheat your oven to 375°F (190°C).
In a large pot, boil the cubed potatoes in salted water until tender, about 15-20 minutes.
Drain the potatoes and return them to the pot. Mash them slightly to break them up.
Add sour cream, ranch dressing mix, garlic powder, salt, and pepper to the potatoes, and mix well.
Fold in the shredded cheddar cheese, crumbled bacon, and half of the green onions.
Transfer the potato mixture to a greased baking dish, spreading it evenly.
Sprinkle the remaining cheddar cheese on top of the potato mixture.
Bake in the preheated oven for 25-30 minutes, or until the cheese is melted and bubbly.
Remove from the oven and let it sit for a few minutes before serving. Top with the remaining green onions.