What is the correct wiring?

Here is how mine was when I took it apart but I think it is a different model.

I would recommend placing it on a wooden desk, plugging it into a solid power strip with a power switch, then hooking it up to the wall (carefully, you now have dangerous voltages that can kill you) The idea of the power strip with a switch is so that you do not actually have to touch the exposed circuits while plugging it in and unplugging it. Some times, the aluminum heat sinks can have voltage on them too that is dangerous.

Use an multimeter with the red and black leads plugged into the correct voltage holes, in Voltage DC mode in the range of 25volts or so (should only be around 16-21vdc I think) and probe the 2 points.

If your reading is a - value, your red and black are the wrong polarity, If you get a positive value, you are correct with the polarities.

Good luck!