How to Make It
Stir together brown sugar, chile powder, cumin, salt, garlic powder, and cayenne in a small bowl. Rub all over brisket, and chill at least 1 hour or up to overnight.
Stir together broth, vinegar, Worcestershire sauce, and 1 cup of the ketchup in a bowl. Place brisket in a 5-quart slow cooker; pour broth mixture over brisket. Cover and cook on LOW until very tender, about 8 hours.
Remove brisket to a cutting board; let stand 10 minutes. Skim fat from liquid in slow cooker, and discard. Stir in remaining 1/2 cup ketchup. Slice brisket against the grain; serve with sauce.