When potatoes are stored in a cold environment, the starch in them turns to sugar. That is why potatoes should never be stored in the fridge but in a cool, dark place. Before cooking, make sure your potatoes are at room temperature, which will turn the sugar back to starch.
ok but that doesnt explain why the supermarket value potatoes taste sweet because they arent stored in a cold environment, they are stored at room temperature in the supermarket and at my home.