Add pineapple to the bottom of of a 5 quart or larger slow cooker.
Sprinkle the sugar on top of the pineapple.
Next sprinkle the dry cake mix on top of the pineapple evenly.
Pour the melted butter on top of the cake mix.
Place a thin clean kitchen towel OR a double layer of paper towels between the lid and the slow cooker insert.
Cook on HIGH for 2 to 3 hours.
Notes
In this recipe I used a 15.25 ounce box of Betty Crocker brand yellow cake mix. Any brand will work however as long as it is designed to make a 13 x 9 inch cake.