Ref to MilktrayUK and the Boeing Doc, I find it strange that Boeing place the GP receptacle on the LH side, mostly they are found RH or centre and as the vehicle plan shows a GPU on the RH side, there must be extra long cables.
Perhaps Hi_Tech could qualify whether similar to other Boeings the GP can be on a service mode to allow cargo door/loading and limited galley power for start up of coolers and of course to get the kettle (rapid boiler) on for the Capt. tea.
I found it distressing to watch on tv, a 'Fireman' climb a ladder at the aft cargo door, mostly unsupported and attempt to unlock, by over-reaching, the door; this raises the question in my mind as to their knowledge of modern airliners if power was not on-line. Also not good was to see so many Firemen standing around with what appears very little direction when the airport could have been made operational earlier by their return to standby.