I've sent packages to Asia via USPS many times with excellent results -- used priority and express services -- but not PRC. Once on the ground in the foreign country, the package goes into the hands of the local postal service or a contract courier. It's extremely reliable in Thailand, but I don't know how exactly it works in China.

However, to send packages to PRC I've used DHL. Prices were superior to FedEx and packages were delivered timely and in good condition. Staff at the US servic point were knowledgable and a pleasure to deal with.