I'm converting an old Radio Shack 12 volt power supply to a 24 volt unregulated power supply and adding an IEC AC connector. The old power cord had only two prongs and there is no chassis ground - the negative output goes right to the binding post. Should I connect the earth ground from the IEC and the negative terminals of the filter caps to the steel chassis? Or can only the ground wire from the IEC be connected to the chassis? What's the correct practice here?