Spray 4- to 6-quart slow cooker with cooking spray. In medium bowl, mix soup, sour cream, chiles and cheese. Arrange half of potatoes in slow cooker. Top with half of sour cream mixture, spreading evenly. Top with remaining potatoes and sour cream mixture; spread evenly.
Cover; cook on High setting 3 1/2 to 4 1/2 hours.
Just before serving, sprinkle top with onions and chips.