Inverter welders are often misunderstood. They still have a step down transformer just ike your traditional iron cored clunker that weighs a ton however there are some smarts employed in the process. Firstly the incoming AC supply is rectified, then filtered via capacitors. The smooth DC is then inverted via a H bridge transistor arrangement at high frequency, typically 25 kiloherz to 100 kiloherz. The output of the transistors feed the step down transformer which is very small due to the high frequency AC. The output of the transformer is then rectified and used for welding. I bet you never considered how inverter welders work but now you know.