Both types run on power from your electric utility, from 110 to 600 volts AC.
Both use the frequency of the incoming power to vibrate the electrode to make and break the arc;
The difference is in how AC and DC machines provide “burning” power to the arc.
An AC head vibrates at 50 or 60 times per second.
An AC machine’s power supply steps the voltage down
to form the arc. The cutting is smoother, more precise. The
Heat Selector adjusts power to the electrode.
The electrode is connected to the positive side of the power
supply; the work piece to the negative side.
A DC head vibrates at at 120 times per second.
The power supply in a DC machine provides full-wave DC
power to the arc. The cutting is not as precise as AC. The
Cutting Power selector adjusts power to the electrode.
The electrode is connected to the negative side of the
power supply; the work piece to the positive side.
The Bottom Line
Because DC power can sustain a larger arc, you can use larger electrodes like square or hex-shaped carbon to burn faster or make larger holes. The quality of material erosion is different.
But power comes at a price. The components in a DC machine cost more than those of a similar- size AC machine, and weigh more.
Which machine is best for you depends on what you need to accomplish on a daily basis.