A separate relay that ( DPDT ) senses the mains turning off can bring the power jack on line without problem or surge protection.... under any load I have tried. I have a transfer switch to go from mains to pj power, and as fast as I can switch it under any load conditions, it just runs with a slight flicker of the lights if I'm slow.
Probably even safer is to use two relays interconnected so one has to drop out for the other to turn on...should be fast enough still to cause no disruption to your gear.
It won't care if those loads are big induction loads or not, it won't care and will adjust it's voltage in a wave or two. No load you can dump on it instantly will remotely compare to the torroid surge start up current... thats the killer. The PJ can't change the freq to the tranny fast, or it is the same thing.
So if you charge independently, and the PJ is on, you can switch back and forth without a problem in my experience.
You will have the expense of keeping the relay alive while the mains are on is the only down side. Just make sure the relay is physically big enough for the contacts to break cleanly before make... and in my experience that should do it.
If you can integrate a small time differential them good, but as fast as I can pull the switch, there have been no problems in the last year or more....
My PJ runs all the time, so it is always available to switch to...... mostly it runs the place, but sometimes when I want to fiddle with the system, I switch it
across... no issues.
If your running the pj in sleep mode, then there will be a delay anyway. It will start up under full load without fuss... I have hit it wih 8kw at a cold start, and it just does not care..... nor do the 002 boards I am playing with and the 8010's
.............oztules