Normal
I'm basically doing the same thing. I talked with Larry(HDPlex) and he said both of the units can run off a single source. I ran into the issue of switching the second HDPlex on(400W unit), which would easily be addressed by a ATX splitter but defeats the purpose of having a direct plug-in unit....so it's either soldering a wire in on the plug-in unit(PSU_On) or building some sort of breakout adapter(this is what I plan on doing by modifying an eBay 90degree ATX adapter). The 400W HDPlex has a separate pin just for PS_On but I don't think the 200W unit does.