On the AC scale a multimeter circuit measures the average value of the rectified waveform (unless it specifically states in the specification that it measures RMS) with the scale calibrated to read the RMS value (about 11% higher than the average value). That's for all frequency components within its frequency response specification.
On the DC scale the multimeter will generally measure and display the average (un-rectified) value.
Thus the voltage you measure from a square-wave will depend upon the duty-cycle of the waveform and its amplitude.
Yes I think you are right . The mosfets feed into a center trapped transformer and the output is stated to be a full wave though so perhaps one is negative . I'll have to recheck now.-thanks
On the DC scale the multimeter will generally measure and display the average (un-rectified) value.
Thus the voltage you measure from a square-wave will depend upon the duty-cycle of the waveform and its amplitude.