A few months ago, I was watching one of Benz Trainz videos where he used an inexpensive DC power supply for his 0-gauge trains. I was intrigued, so I bought one like this: a YUNBO Adjustable Voltage Power Supply Adapter AC 100-240V to Variable Voltage DC 3-12V 5A 60W.
This worked well for a little while, but the 5-pin, B5K on-off potentiometer is not very robust, didn't last long, and I discovered that it is really a PITA to replace. The enclosure was not easy to open, and after an extensive web search, I realized that the pot is a real specialty item, with a long shaft, 3 long pins and 2 short pins for direct mounting on a PCB. I wasn't able to find a replacement, so I just bought another power supply.
However, I thought I'd do a little experiment to see if I could repair the old power supply. So I opened up the case (not very easy), and desoldered the pot, which is physically connected to the PCB via the 5 pins. I wired-in a new SPST rocker switch and a new 3-pin B5K pot with connections to the PCB.
See the picture below for the hasty, experimental setup. The red and black wires from the switch are routed through the pin openings and are soldered to the terminals at the backside of the PCB. Likewise for the blue-green-yellow wires from the new pot.
Eventually, I will install all of this is a new enclosure. The remote switch and pot configuration will allow for an easier replacement the next time either of these components fail. Hopefully, the power supply will last longer and will be more reliable.