Switch-Mode Power Supplies.

[Yorkie]

Indeed, David, of course: a silly over-sight my me!
Apologies Joe.

Al.

No call for blush's or apologies Al - I only have the sketchiest knowledge of SMPSs. If we knew a bit more about SMPSs, we'd know whether the waveform that Joe sees means that there's a fault, or that it's working perfectly! To quote Erasmus of Rotterdam: 'In the kingdom of the blind, the one-eyed man is king!' (There have been some useful articles in electronics magazines about how to convert PC SMPSs to high current bench power supplies).