If the enclosure is a host mode device, effectively making the PSP a client device, is this no different than what you could do with the 770. It would make no sense to me that the enclosure wouldn't have +5 volts sending out on the line to the PSP.

Clarification? Anyone?

*Edit*

According to http://www.beyondlogic.org/usb/otghost.htm :

A dual-role device needs only source a minimum of 8 mA on Vbus

The question is now: Would 8mA be enough to enable the 770?