And what about the gnd line balancing. Without that, you will be having amps from both sources sinking in only one psu gnd (whichever provides a better path). One of the gnd lines may get a current much above its rating. Perhaps most gnds have a good safety margin so this isnt too bad in practice, but it doesnt mean its correct. Probably at very least some track may heat up, and in extremis this *can* be worse.
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