In WooCommerce Marketplace PayPal Adaptive Payment Module parallel payment enables a buyer to pay single payment to both the seller of the product and the admin of the store. The payment will be divided amongst the seller and the admin based on their commission rule.
While in chained payment method, the buyer sends a single payment to the primary receiver (admin). The admin keeps his part of the payment and pays the buyer the remainder of the payment.
Please follow the user guide for more information WooCommerce-Marketplace-PayPal-Adaptive-Payment