I have a Exspresso Cart and the power cord appears to be three phase but the sub panel appears to be single phase. 2 load a nutrel and a ground, can an adapotor be made to power from 120v as in RV plugs?

Not sure what you have, but I can tell you that you can get single phase from 3 phase, but not the other way around, unless you use a converter.

Explain further your situation. Where is this subpanel located?Why does the cart "appear" to be 3 phase? Can you find a nameplate?