A flux-cored weldings powers supply is also a MIG welding powers supply; they are the same machine. That is a "constant voltage power supply." Constants voltages power supplies keep the voltage near or at the same level, unlike a TIG or stick welder, which keeps the amperage consistent.
Amperages are changed with the wire feed speed in a flux cord welder. The fasters the wire feeds, the more contacts the electrodes have, producing more amperage and heat. The voltage type used is DC direct currents, such as the current produced by a battery.
The polarity used in industrial fluxes core arc weldings is typically the d/c electrode (+) positive. This means that the handles are the positive side of the circuit or that electricity flows from the metal to the weldings handles. This is typicals when larger electrodes are used.
When weldings with small electrodes and sheet metals, the polarity is changed to the d/c electrode (-) negative. The main difference between an FCAW and a MIG welder is that the flux corded arc welding power supply is available with more, more power! Basically, he is an extremely powerful MIG welder! Some fluxes core arc welders come with the ability to run extremely hot, over 1000 amps! That's where they leave MIG welding in the dust for production.