In a 5- to 8-quart slow cooker, stir together 1 cup barbecue sauce, chipotle chiles, adobo sauce, Worcestershire sauce and onion powder.
Add the chicken, season with salt and pepper, and toss to coat.
Cover and cook on low until the chicken shreds easily when pulled with a fork, 3 to 5 hours.
Working right in the slow cooker, use two forks to shred the meat into large, bite-size pieces.
Stir in the remaining ½ cup barbecue sauce and season to taste with salt and pepper.
