The power supply is a dynex 400. I have spliced into SATA power cable. The computer on the left has the serial cable attached and everything is working correctly. The computer on the right is only there to turn on the psu.
As you can see from the warning note at the top of the adapter’s product page, using power leads longer than a few inches can cause LC voltage spikes that exceed the maximum voltage rating of the part, which can permanently damage it. Your leads are a few feet long, so I think this is likely what happened with your adapter, though I would expect it to be getting at least a little warm if it was damaged in this way. When using long power leads like this, we recommend you take steps to prevent these spikes from reaching the adapter (e.g. connect a large electrolytic capacitor across power and ground close to the adapter).
There’s not too much to the board, so if this isn’t the problem, I don’t really know what else to suggest. If you want to have us take a look at it, you can contact us directly and we can give you an RMA number.
- Ben