If you are using the instek you should be able to just reverse the banana plugs on the power supply. Where you have the red to red and the black to black, just go red to black and black to red. If you have one of the twin banana plug assemblies that plugs into the PS, just turn it upside down and plug in.

Now, you say that the clip cord works.....can you reverse the clipcord " flip it upside down" and make it run? if it runs reversed, then I would think there is a problem with the machine' s internal wiring....things happen. If it does not run reversed, then you can try the " flipping the banana plugs" thing I suggested.