In a large saucepan, melt the butter over medium heat. Add the onion, season with salt and pepper and cook, stirring, until tender, about 5 minutes. Stir in the chili powder and cook for 2 minutes. Add the potato and chicken broth and bring to a boil; lower the heat and simmer until the potato is tender, about 10 minutes.
Stir in the corn, chicken and green beans and cook until heated through. Season with salt and pepper. Serve with the sour cream.