In the U.S.A. this would be a major code violation, as I commented.
I have multiple 2500kva transformers feeding different areas of my plant, 2 are close enough that I thought I would see what would happen if I hooked this configuration up pulling 20+ amps into my load. using the trip curve for the breaker I set it at 25 amps no problem, after about 3 minutes it tripped.
What I did notice was that it spiked my monitor for a phase imbalance. If I would have loaded it any further I would have shut down the transformer that I returned the neutral side.
This is set for 100 amps so I am not sure why a 25 amp load gave me the first warning level. the meter only showed minor leakage and that is normal for this size system. Now I can say it is dangerous coming from different systems.
I thought I might see a mild increase in leakage from the transformer supplying the power but my equipment did not record this. I did also see on the recorded data oscillations of voltage across the load. this is a liquid load (brine type) rated at 1000 amps so it did not even get warm enough to boil. Boiling will cause oscillations.
With this information, I believe this could damage the electronics in the charger especially as the load changes on the transformer that connects to the neutral. So I still think this crazy and unsafe.