Combine chicken, potatoes, bell pepper, and onion in a slow cooker.

Stir together chicken broth, curry powder, curry paste, cumin, 1 teaspoon salt, and cayenne in a bowl and pour over ingredients in the slow cooker. Mix everything well with a wooden spoon.

Close the slow cooker and cook until chicken is tender, 4 to 5 hours on Low or 2 to 3 hours on High. Add coconut milk 15 minutes before the end of the cooking time and continue cooking until heated through. Season with salt and pepper and sprinkle with chopped cilantro to serve.