I don't know why you say "after 5.3".
The External Power feature when the GSX jetway connects, is something that on airplanes flagged as having a custom electrical system ( and the PMDG surely all are ), GSX NEVER tried to set any external power to them, leaving its implementation to the airplane developer, on the assumption it won't be safe or might not work trying to do this on an airplane with its own custom electric simulations.
That's why GSX only does this on default/freeware airplanes that most of the time use the default electrical system so, GSX simulates this by setting the default battery voltage variable while the jetway is connected. It doesn't do *anything* on airplanes flagged as having a custom battery system so, if the airplane developer doesn't add support for this in its own code, the External power provided by the GSX jetway won't do anything. It has been like this since this feature came out.
I don't know about QW, but I'm fairly sure PMDG never supported this feature so, unless you did/downloaded some kind of extra code (possibly Linda ?) that read the GSX status and simulated that on its own, it's not possible it would ever worked on PMDG before, that's why I found strange you'd say "after 5.3", perhaps you forgot to reinstall that add-on script in 5.3 ?
Instead, it's entirely normal it would only work with Aerosoft planes, because I'm sure they support the GSX External Power feature, same as Leonardo MD-80 and FS Labs.
