I thought I had an answer but.... just to be clear: ZW-L analog meters read 15 volts and 4 amps, digital meters read 0.73 amps (hard to read) and 11.29 volts???
Are you sure they are reading at the same electrical points? There has been a lot of discussion on the forum on chopped sine waves and how that impacts various meters. However, Seems hard to imagine chopped sine waves (if that is what the ZW-L produces) can explain 4 amps versus 0.73.