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.
I have edited my earlier post, with a photo. You are correct that on narrow bodied aircraft, this connector would be on the LH. For wide bodied aircraft, one connector cannot supply enough power for the full electrical loads. Calculating the length of cables and power losses for each aircraft model using the stand would be part of the stand design process for a fixed installation!
I should add that the system includes a feedback mechanism controlled by the aircraft, so the supply is de-energised if the load is dropped by he aircraft electrical system. The common on-line reference sites do not describe systems for fixed installations, or list relevant photos. System descriptions can be found on supplier websites.
For starting the 787 engines with the APU unserviceable, a third GPU is recommended. This connection is located behind the wing, serving the aft electrical bay, where the main generator feeds connect into the power system. Most likely a diesel power cart would be used in that scenario, but I do wonder about the operational procedures needed with ground staff working behind running power plants and main gear.
