This might not be the best answer but it has tested ok so far. Maybe someone with a better skill set can improve on it. I have three PS3 engines with the wireless tether. Two have been very reliable to date but the third is a headache. After a few laps at speed with a decent consist it will stop dead, in need of a connector reseat and restart.
My beef with the PS3 steam tether has always been that the connector is part of the load path from the engine to the tender. It's a good concept except that the plastic plug connection isn't quite reliable enough to keep the connector from unseating. Once it comes loose even a little it will eventually walk down the post until the connection fails. So, any simple device that prevents the tether plug from sliding down the post should work. One good approach is the zip tie but I wanted to try something else.
In the first photo below you can see that the post on the scrap tender has an "I" shaped cross section. So I was thinking that something could be pressed into that forward slot that would stay put and help keep the connection secure. The other ingredients for the fix are machine screw and the tiny rat tail file. Hard to see but the rat tail file is used to create a very small notch in the tether opening opposite the forward slot in the post. Just like with the zip tie carefully lay the tender and engine on their sides. Seat the tether plug. Insert the machine screw into the opening. It should be easy to torque but still tight. Once in place (second photo), the screw threads grip the tether and bite into the soft metal on the post. Pretty sure that's not going to come loose. On my problem engine I actually used a much smaller #0 x 1/4 and I didn't have to file the notch. Worked great but I actually like the look of the bigger machine screw in the photos.
You can take it apart of course but not with the train on the track. Like the zip tie, the tender and engine have to be handled as a unit after the fix is made. If MTH were to modify the post with a wire spring in the tender post slot that would be even better.