I'm going to preface this by saying, to some extent, both @Juan Wayne and @panther_king are right... and both are wrong a bit. (take that, Solomon!!) That said, I'll probably get slammed by both parties involved...let the food fight begin (j/k!!!) If "ideal power supplies" are connected in parallel to an "ideal load" and there is a difference in their voltage output, there will be an infinite current flow in between the power supplies and something is going to go 'poof' ... it's basic math. In the ideal world, two PSUs with identical outputs could be connected, but they'd have to remain perfectly in sync.... and nothing is that perfect in the real world. To avoid the smoke-scenario in the real world MOST power supplies are set up with a current limiting resistor (or some other functionality) that takes the voltage drop due to the supply-to-supply differential. In the dinky 100-600 mA supplies that we are using on our boards, the result if this goes bad isn't massive.... yes, something will smoke if the differential is big enough, but it isn't a huge physical risk. In larger supplies, tho, this can be a thing to do with caution. I used to work around 100+ amp, 5 volt supplys daily at Tek and Mentor Graphics, and when they found a reason to tie them together they'd follow a very rigorous protocol that involved setting one supply as a Voltage Master (constant voltage) and putting the other in a Constant Current mode, such that the second unit did not try to control it's own voltage output. If you get 2 100 amp supplies fighting over the voltage reference, the room is going to smell of burnt FR4 in no time flat. Bottom line : don't current double unless the PSU manufacturer sez it's ok, and even then get their home office number for the fire report. I have wondered whether the 'current doubler' cables supplied from pedal-PSU makers contain a current limiter of some sort, or do they build in a limiter in their individual outputs? I sincerely doubt that plugging in one of those current-doublers triggers an automatic Master/Follower configuration of the individual supplies. That would require a little sensing circuit that I do not see when I've looked at some of their layouts. "Not all analogies are equal. Some are more equal than others." - - blatantly plagiarized, cut from the herd, butchered, and re-used from George Orwell' Animal Farm. Those true-all-wheel-drive vehicles have lots of feedback and controls to ensure that vehicle is going to continue on the straight and narrow. Things as simple as putting on a spare of different diameter could really mess them up if this were not the case. That is a very different scenario from the connecting the outputs of two power supplies. When the power in play is large and the consequences are bigger than just "I smoked my PSU", There generally are significant controls put on one or both of the power supplies, per above. And just to be pre-emptive, I offer that it is also different from the scenario of connecting two batteries in parallel. Batteries are (generally) subject to precepts of electrochemistry that offer some builtin tolerance of parallel connection... also, a number of batteries contain materials which tend to limit the current output.