Add the cubed potatoes, diced onion, chicken broth, garlic powder, salt, and pepper to your slow cooker and stir to combine.
Cover and cook on low for 6 hours or high for 3-4 hours, until potatoes are very tender.
Use a potato masher to mash about half of the potatoes directly in the slow cooker, leaving some chunks for texture.
Stir in the milk and softened cream cheese until fully incorporated and creamy.
Add the shredded cheddar cheese and stir until melted and smooth.
Serve hot, topped with crumbled bacon, extra cheese, and fresh chives.