Combine the chipotle with adobo sauce, marmalade, chili powder, garlic powder, vinegar, honey, chicken broth, and oil.
Wash chicken and pat dry; sprinkle with salt and pepper. Arrange the chicken breasts in the slow cooker; pour marmalade mixer over all. Cover and cook on LOW for 5 to 7 hours, or until chicken is cooked through.
Put the chicken breasts on a plate; cover and keep warm. Pour the liquids into a saucepan and bring to a boil over medium-high heat. Reduce heat to medium and simmer for about 5 to 7 minutes, until slightly reduced. Combine the cornstarch with cold water until smooth; stir into the sauce and continue cooking, stirring, for about 1 minute longer, or until thickened. Serve the chicken with the thickened sauce.