I want to know the answer to the following question:
What can devices request?
All the background I'm provided with is that "In July 2012, the USB Promoters Group announced the finalization of the USB Power Delivery ("PD") specification, an extension that specifies using certified "PD aware" USB cables with standard USB Type-A and Type-B connectors to deliver increased power (more than 7.5 W) to devices with larger power demand.". Is that enough to answer the question?
Answer: no