In a large pot, heat olive oil over medium-high heat. Add onion and celery and sauté until just translucent, about 3 minutes. Add garlic and cook for 2 more minutes. Stir in sweet potatoes, vegetable broth, coconut milk, chili powder, paprika, cumin, salt, and pepper. Bring soup to a boil and reduce to a simmer. Cook for about 20 minutes or until the sweet potatoes become fork tender.