I opened my Techie up to check the 0V tag and indeed it had been placed on the top-right post (i.e. the wrong one) by Timestep. I re-routed the cable slightly and attached the tag to the correct bottom-left post. This cable is now quite short and just reaches the SR5 PSU with little to spare, just as I want it for least voltage drop. Things are sounding very good indeed.

I've now received a 4-pin Neutrik connector and will fit this next, to replace the 5/2.5mm PSU plug.