Place the diced potatoes, onion, garlic, chicken broth, salt, and pepper into the slow cooker.
Cover and cook on low for 6 to 7 hours until the potatoes are very tender.
Use a potato masher to break up some of the potatoes for a thicker texture, leaving a few chunks.
Stir in the heavy cream and half of the shredded cheddar cheese until the cheese melts.
Ladle the soup into bowls and top each serving with the remaining cheddar cheese, crumbled bacon, sour cream, and sliced green onions.