Place the cubed potatoes, diced onion, chicken broth, garlic powder, salt, and black pepper into the slow cooker. Stir to combine.
Cover and cook on low for 7 hours until the potatoes are very soft.
Use a potato masher to break down the potatoes until the soup reaches a thick but chunky consistency.
Stir in the heavy cream along with 1 cup of the shredded cheddar cheese until the cheese melts into the soup.
Ladle the soup into bowls and top each serving with the remaining cheddar cheese, crumbled bacon, sliced green onions, and a spoonful of sour cream.