Mix brown sugar, chili powder, salt, pepper, garlic powder, and onion powder in a small bowl. Rub each rib with dry rub mixture until thoroughly coated. Let rest for 10 minutes.
Mix BBQ sauce and liquid smoke until well combined.
Place ribs in the slow cooker and pour BBQ sauce mixture evenly over ribs.
Cook on Low until ribs are tender, 4 to 6 hours.
Set an oven rack about 6 inches from the heat source and preheat the oven’s broiler.
Remove ribs from the slow cooker and baste with remaining BBQ sauce.
Broil ribs in the preheated oven for 3 to 5 minutes on each side.