Peel and slice sweet potatoes. Drain the pineapple juice from the can into a liquid measuring cup. You'll have ~1 cup of pineapple juice. Then add the 1 cup of water to the liquid measuring cup. Set aside.
Mix two tablespoons of cornstarch with a little water and mix well. You shouldn't need to add more than 1-2 tablespoons of water. Add sliced sweet potatoes to the crockpot then add all other ingredients including cornstarch. Stir all the ingredients together.
Turn on high and cook for 3 hours. It's tender at 3 hours, but if you like your yams even more tender then you can cook longer (up to 4 hours). *At the 3 hour mark, I would recommend to check it every 30 minutes until it's tender the way you want it. Just to make sure it doesn't turn to mush :-).
Notes
See "Variations" if you don't have pineapple juice - What if I don't have pineapple juice?Each serving, ½ cup, has 6 grams of added sugar. Nutritional values are approximate and based on products used.