Place sweet potato and Yukon gold potato in a medium saucepan; add water to cover. Bring to a boil; reduce heat, and simmer, uncovered, 20 to 25 minutes or until potatoes are tender. Drain. Remove half of potatoes and set aside. Mash the remaining half of potatoes with a potato masher; set aside.
Heat olive oil in a Dutch oven over medium heat. Stir in onion, bell pepper, and celery. Cook 8 to 10 minutes or until vegetables are tender. Stir in mashed potato, corn kernels, and next 7 ingredients. Simmer, uncovered, 15 minutes. Add reserved potatoes and cook 10 minutes or until soup becomes thick. Ladle into 5 individual bowls. Garnish with fresh chives, if desired.