In general I have found the typical “universal” (100-240V) brick gets QUITE hot when used at 220/240V.
I’m in 110/120V USA but I work a tradeshow in Europe and the last time we had some monitors with bricks that said they were fine at 100-240V, but I think they started to overheat, because the ones with airflow around worked fine (still open on all but one side, and sitting on wood), but the ones without airflow around went bonkers (generated noise on the monitor) until we put them on step-down transformers and fed them 110V instead.
I’m not engineer-y enough to know whether it was some kind of design issue on those PSUs (this was the first time I’ve run into such a problem - all our other equipment was fine), if the “optimal” conversion voltage is closer to 100 then 200, or what. All I know is they worked much better with lower voltage.
I’m not sure how hot is my Drobo’s PSU (it’s under the desk) but my company laptop’s PSU runs mighty hot. If you’re working on the laptop while it charges it reaches the “almost too hot to touch” temperatures. And it’s like this since almost five years now, working just fine.[hr]
Generally speaking, the switching mode PSUs are quite complicated beasts. There shouldn’t be any obvious dependencies between input voltage and the temperature / efficiency, from what I know (but I might be wrong). That would be definitely the case if there were linear voltage stabilizers used (the more voltage difference - the more power to literally waste as heat in the conversion) but they are very far from that. Your observations are quite surprising to me as the lower voltage means higher input current but I think due to the relative complexity of the switching-mode PSU’s design, it all “depends”. Anyway, no need to worry as long as they’re working fine and used within their operating parameters.
Thanks for the technical info Zbig - I think likely this particular company used “too cheap” PSUs - or they were just plain overheated - the room they were in was warm, but not hot - definitely within normal ambient operating temperatures, but tradeshow power is notoriously dirty and unstable, so it’s probably just one of those situations where it was just slipped off the edge of OK.