USB PD when it comes to systems is typically found on laptops in order to allow them to be charged via USB-C. Some USB-C connectors only provide basic 'legacy' USB power without supporting the USB PD spec at all. But not every device with a USB-C connector is required to support being powered that way, and not every device with a USB-C connector is required to support providing that much power. The spec currently allows for up to 100W.
USB Power Delivery is a specification that allows sending various levels of power over USB-C connectors.
