Disconnect the topper is the first thing I would do. Then standard computer troubleshooting starting with the power supply.

I agree about opening a service ticket with JJP.

If you’re continuing on your own can you explain the part I quoted in a little more detail? I’m reading you hooked up the topper to the blue wires and used the paperclip jumper but that doesn’t make sense because your topper should be disconnected now.

In Butch’s video about jump starting he instructs you to hold the paper in place until you see text, then remove it. What he doesn’t mention is if you hold it longer than four seconds the power supply interprets this as an OFF signal and will shut down. Imagine you’re starting your computer. Press the button and let go, don’t hold it down.

You can also test the power supply alone if you disconnect the large (20 or 20+4 pin) connector from the PCB and then jumper using Butch’s method. Your power supply fan should come on but nothing else will since it’s disconnected.

This is similar to the tester I use: https://www.amazon.com/Computer-PC-Tester-Connectors-Enclosure/dp/B076CLNPPK
Note that if you use this one your 12v2 will show low since it’s not provided by that connector.