2) Current sharing. Whichever supply has a slightly higher voltage will take all the load (and if the load is too high, it will damage the SMPS). The power supplies will not equally share the current demand of the circuit - instead one will go into runaway mode, taking it all. If that one then shuts down from current overload, all the current will suddenly be dumped on the second one, which will also then have to pump current into the other, now shutdown power supply