But then look at what is being done with this supply (or supplies in this instance).... whether they are a group in series or better yet one switching power supply of ample power, the ultimate use is as if it is a linear supply of varying load. If we were charging a battery - OK; or a fixed load - OK. But he's attempting to run an electric motor with a group in series of switching supplies. They still will need to be filtered as if it was a linear supply and even very much more so in this instance. These type supplies are designed for specific loads and specific variables in load but keeping the load demand in mind as has apparently been accounted for, all we need to do for Adrian is help him quiet down the effects of running a DC motor on his group of switching power supplies..
I will respectfully bow out of this....
Sorry Adrian, just attempting to help you out. My experience with power supplies of all types goes all the way back to the thyratron tubes that Monarch used in their EEE lathes, which I serviced and maintained for years. Computer supplies are a shortcut in technology to satisfy a narrow line of demand and price. 'Simple' linear supplies are not so lost in the mist of current thinking - might be some lack of experience or respect.
Thanks,
Bill C.