Please forgive me if you know this already. On the Rollei TLRs of the 1960's there was a surround on the PC port with a little lever that was for the Rollei locking PC connector. Push the lever, insert the cord, and release the lever... and there was a spring (I seem to recall) that held the pc cord in place securely. Push the lever to remove. A regular pc could be used but would not, of course, lock. I seem to recall that the Rollei flash bulb holders of that era came with the Rollei locking pc. I suspect that you are referring to later Rollei strobes, which I have no experience with, but would not be surprised if they had just a standard pc since they were manufactured, as I recall, by a number of companies and OEM'd under the Rollei label (probably others too) were intended for applications beyond just Rollei cameras. As you can tell, I have little experience with most "European" flashes but did use 1970/1980 era Braun in the past and I think they had the same design/application philosophy.