http://www.datasheetarchive.com/pdf-...DSA-369352.pdf

My guess is that the part above might be similar to what is in the
welder. I like the explanations of the caps used for filtering
(especially seeing the choke in the circuit). Another way of
explanation might be that the caps help keep a small forward voltage
across the rectifier to keep it from cutting out. (See voltage vs.
amp curve) The welder might work without the caps, but it could have
a noisy erratic arc and you might have more problems with sticking
electrodes when you got too close using SMAW.

Now I’ll return to my seat in the peanut gallery!