For these dual conversion phenomenon dunnah forget to take into account the
efficiency of the "modified sine wave" converter 12vDC-> 120vac.  Check the
waveform before deciding that cheaper is better.  The computer powersupply
may have some limitations regarding waveform.  It expects a pretty clean
sinewave.  Most inverters do a stepped approximation of a sine wave.  Check
before you plonk down those IBM dollars.

pensioner  (MSEE,MSCS, and still can't find a decent job)