Slow Cooker: Put potatoes in the slow cooker along with ¾ cup chicken broth, 1 ½ teaspoons garlic powder and ½ teaspoon onion powder. Cover and let cook on HIGH 3-4 hours or on LOW 6-7 hours.
Combine: Remove cover and add½ cup + 2 tablespoons sour cream, ½ cup plain greek yogurt, ½ cup butter, ¼ cup milk, ¼ cup ranch dressing, 2 ½ teaspoons kosher salt and ⅛ teaspoon ground black pepper. Use a potato masher to mash everything together until the consistency is smooth (alternatively you can use a hand mixer).
Adjust: Taste and adjust the salt level or any other ingredient, per your own preferences.
Storage: Store in an air-tight container for up to 3-5 days in your refrigerator.
Make-Ahead + Reviving: Make these mashed potatoes the day before and place in a casserole dish or dutch oven. Add additional cream and butter, stir, and place in the fridge over night. Revive them the next day by adding additional butter on the top and warming them in the oven or over the stovetop.