Multiprocess welders that offer arc, MIG and TIG functions in one unit are ... “They’re very portable and can run off either 120 or 240 volts.” Depending on amp-capacity, a 10 lb.

(Use science for peace please!) I did really need a spot welder though, and there was no shortage of examples of people who had built their own from supercapacitors, typically in the 500 F range.