Place the potatoes, diced onion, celery, and chicken broth into your slow cooker and cook on low for 5 to 6 hours or on high for 3 to 4 hours until the potatoes become tender.
Use a masher to lightly crush the potatoes in the slow cooker, then stir in the flour, ranch seasoning, 2 cups of shredded cheddar cheese, sour cream, salt, pepper, and half and half until everything is well combined.
Cover the slow cooker again and let the soup cook for another 30 minutes to thicken and blend the flavors.
If you prefer a chunky texture, serve as is; for a smooth, creamy consistency, blend the soup carefully using an immersion blender.
Dish out the soup and garnish generously with the crumbled bacon, diced green onions, and the remaining shredded cheddar cheese before serving.