Heat oil in a large skillet over medium-high; sear beef in batches about 6-8 minutes total until browned on all sides. Transfer to slow cooker.
Sauté onions and peppers in same skillet about 5 minutes until softened; add garlic and cook another minute. Transfer to cooker.
Add black beans, pinto beans, tomatoes, tomato paste, broth, and chipotles.
Stir in chili powder, paprika, cumin, brown sugar, salt, and pepper until combined.
Cover; cook on low 8-10 hours or high 4-5 hours until beef is tender and flavors meld.
Serve hot with cornbread, shredded cheddar cheese, sour cream, and diced jalapeños on the side.