Heat oven to 375, line a rimmed baking sheet w/ foil, spray foil w/ cooking spray. Place wings on baking sheet. Bake 20 mins, drain off any fat.
In a slow cooker, combine plum sauce, butter and 5-spice powder. Stir well. Add chicken and stir to coat. Cover cook on high 3-1/2 hrs, or on low for 2 hrs. Sprinkle w/ scallions. Serve sauce w/ wings.