Energy efficient power supplies won't run on inverter

We have a Poweredge R815 with redundant energy efficient power supplies, which we are trying to power from a "modified sine wave" power inverter. (This is a mobile military application.) The energy efficient supplies in the R815 do not want to run on the modified sine wave. We looked at the waveform from the inverter and it is more like a stepped square wave - there is really nothing "sine" about it. I was wondering if Dell can provide a non-energy efficient power supply for the R815 that would play well with the inverter waveform. Thanks!