I sometimes use older Speedotron Black Line pack-and-head systems such as the 805 and 2403B, on which I've been able to find good deals on eBay. Initially, I used cheap eBay wireless triggers, but reliability was lacking. So, I bought into the RadioPopper JrX system.
When I first got the RadioPopper hardware, I thought I had gotten a defective receiver, but the truth is more complicated. I first verified that the transmitter could talk to the receiver. This is pretty easy to do via the on/off/test buttons and the LEDs. The hitch was that the receiver wasn't firing the strobe. I tried various means of connecting the JrX Studio Receiver to the Speedotron 805 power supply. I tried the included stereo 1/8" phone cable and 1/4" adapter. I tried a mono 1/8" to 1/4" cable. Nothing worked. The strobe never fired.
Searching the web, I frequently came across two ideas: reverse polarity and electrical isolation. Since a Wein Safe Sync isn't cheap, I decided to try the polarity first. After some quick trips to my local electronics geek supplier and the home center, I had the parts I needed. Time to solder. For the 805, I built a 1/4" mono female to 1/4" mono male adapter that reversed the tip and ring. For the 2403B, I made something similar that went from 1/4" mono female to 2-prong polarized household plug. Results were disappointing.
So, I trudged out to my local pro photography store and plunked down my money for a Wein Safe Sync MMSS (1/4" mono). Plugging the JrX via the supplied cable into the Safe Sync and 805 resulted in failure. Inserting my polarity reversing adapter between the Safe Sync and the 805 fixed the problem. Yay! A mess of wires, to be sure, but I can deal with that. A similar setup worked with the 2403B.
On some days, I've been able to get the 805 to flash without the Safe Sync, but it's not reliable. Frankly, it's probably not safe, given the voltages.