Add chuck roast to the insert of slow cooker. In a 2 cup measuring cup stir together beef broth, apple cider vinegar, garlic, chilis, adobo sauce, cumin, chili powder, oregano and salt. Pour into slow cooker and cook on low setting for 8 hours.
Shred beef in the slow cooker using two forks. Serve barbacoa with a drizzle of additional sauce.
Store in an airtight container for up to a week in the refrigerator or in the freezer for a few months.