Answer:
Upstream partners are those suppliers who provide raw materials for a firm to produce something. In other words, the upstream supply chain delivers the inputs to be used in the production process.
Downstream partners the suppliers who deliver finished goods from the firm to the clients. The downstream supply chain distributes the ouputs of the production process of a firm.
For example, the upstream partners or Amazon are the companies that deliver goods to the Amazon warehouses, while the downstream partner is mostly UPS, which transport the orders to the customers.
Value delivery network is a better term because it's definition includes both upstream delivery and downstream delivery. It is understood that both sides of the coin produce value, and are interrelated, hence the words that make up the term.