Place bacon in a large skillet and cook over medium-high heat, turning occasionally, until evenly browned, about 10 minutes. Drain bacon slices on paper towels; reserve drippings in the pan. Crumble 6 strips of bacon, saving 3 for garnish.

Heat bacon drippings over medium-high heat. Cook onion in the hot drippings until soft, about 5 minutes.

Transfer potatoes, crumbled bacon, onions, and garlic powder to a slow cooker. Pour broth over the top. Cook on Low until potatoes are tender, about 6 hours.

Whisk half-and-half and flour together in a bowl. Add to the slow cooker and whisk to mash up some of the potatoes. Stir in 3 cups of Cheddar-Monterey Jack cheese blend. Mix until cheese is melted and fully incorporated.

Crumble remaining bacon. Top with remaining cheese, crumbled bacon, and chives before serving.