Put the beans in a large wide pot or Dutch oven and cover with cold water by 1 inch. Bring to a boil, then remove from the heat and let soak 30 minutes; drain and rinse.
Return the beans to the pot and add the bacon, onion, chili powder, Worcestershire sauce, chicken broth and 4 cups water. Bring to a simmer over medium-high heat, then reduce the heat to medium and simmer 30 minutes.
Add 1 teaspoon salt and reduce the heat to medium low. Cover and simmer, stirring occasionally, 1 1/2 more hours. Partially uncover the pot and continue simmering, stirring occasionally, until the beans are creamy and the liquid is thick, about 30 more minutes. Add the vinegar and chives and season with salt.