As preparation, chop the potatoes, sweet potatoes, garlic, jalapeno, onion, and green onions.
Add the sweet potatoes, potatoes, onion, garlic, ½ of the jalapeno, 2 cups of corn, seasonings, and the broth to the slow cooker. Gently mix to ensure everything is covered by the liquid (if not, add more stock or add water so it's mostly covered with just a few pieces poking out).
Cover and cook on high for about 3 hours or until the sweet potatoes and potatoes are fork-tender. Optionally, stir the ingredients halfway through cooking.
Use an immersion blender to partially blend the soup, leaving some chunks of sweet potatoes and blending to your desired consistency. Combine the milk and yogurt with the vinegar, then stir them in. Add the remaining 1 ¼ cups of corn as well. If needed, thin out the soup with another splash of broth.
Adjust seasonings as needed. Mix in the leftover diced jalapeno or use it as a garnish. Top with green onion before serving.
Notes
1 WW point per serving when divided into 6 even servings.