Options for adding add-on charges Access Purchase Order Entry (PO20.1). Select the purchase order that requires add-on charges. Note: A purchase order must be added before you can maintain the AOC spread. To add add-on charges (AOC) to a purchase order header, click the Header button. Use the following guidelines: Miscellaneous Add-On Cost Type add-on charges for a purchase order. Add-On Cost Spread Change the way add-on charges (for a purchase order) are dispersed to the purchase order lines. Select the Change form action. Release the purchase order.