Arrange the chicken breasts in a 6-quart slow cooker.
Whisk the enchilada sauce, tomato paste, ancho chile powder, cumin, garlic powder, salt and broth.
Pour the sauce over the chicken, cover and cook on low until the thickest breast reaches 165°F, 4 to 5 hours.
Move the chicken to a shallow bowl and shred it with two forks.
Skim the sauce, stir in the cider vinegar and return the chicken to the cooker.
Cook on high uncovered for 10 minutes, then cool or use the chicken with enough sauce to keep it moist.