If a person is using two different transformers and getting sparks on the blocks, there is a test for that, but the remedy is to turn the plug around in the receptacle. If the insulated or isolated block sparks when a train enters, why not simple turn one plug around, and save doing the test? I’ve fought that stupid spark for a 3 months, but after turned one plug around, no more problems! Jake
At least you’re using two different transformers, which means that they and your wiring are protected by the circuit breakers. But, unless you set them very close to the same voltage, you will still get some arcing and pickup erosion, even if they are in phase. It’s better to avoid running across gaps between different transformer outputs at all.