A plasma cutter uses high voltage/high frequency to superheat air (or oxygen) to the 4th state of matter, which is plasma. The plasma arc then cuts through anything that conducts electricity.
An arc welder will have something on the order of 40 - 70 open current volts, and when the arc is struck the voltage drops and the current rises to where you have the control set. I don't have any plasma cutter specs in front of me, but it seems like a plasma cutter generates 400 volts at a high frequency like 1000 hz. Again, I am not sure about the plasma cutter specs, so someone needs to jump in here to straighten me out.
However, to answer your question, I do not believe there is any way to use an arc welder power supply to operate a plasma cutter.
