I've tested another +5V Switched-Mode Power Supply and found it does not bother X-10 or Insteon signals. It's the ETA-USA WCS10-05SX carried by Mouser Electronics (PN 618-WCS10-05SX). Mouser carries other voltages in the same series from this manufacturer - I presume they will be equally PLC-friendly.
I've added the results to...
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