Video I saw had the Tech 2 reboot after the starter cranked. Even with the 12vDC cord plugged in, the Tech 2 tries to draw power from from the OBDII port first. As long as there was power detected from the OBDII port, it would not kick over to the 12VDC feed from the other power supply. The switched extender cuts the power coming through the OBDII port, but the rest of the data does its thing. Since the power is cut off from the port, the Tech 2 will run off the 12VDC supply.
This may only be with the clones... Maybe it was only an issue with older clones, that has been since resolved? The video was from 2020. Maybe the problem has been fixed by Vetronix already?
The guy in the video found that his rebooted when initiating the engine cranked over. The switch seemed to solve that. For about $11, i figured it would be good to have if it kept the tTech 2 from rebooting during a diagnostic session that requires starting the engine.
Here was the video...