SMPS in series connection

GA from me.

its also possible that there may be some oscillation between the seperate power Supplies.

As Del says, check the PSU manual. Most SMPSUs have isolated outputs, but if not you're on a non-starter.

You may be able to stabilize the outputs if the PSUs have voltage sense inputs.

Run a string of three 1k resistors from the +ve sense input of the 'top' PSU to the -ve sense input of the 'bottom' PSU. Connect -ve sense of top PSU and +ve sense of middle PSU to junction of top & middle resistors, -ve sense of middle & +ve sense of bottom PSUs to junction of middle & bottom resistors. Also connect +ve sense of top PSU to +ve of load, and -ve sense of bottom PSU to -ve of load. It may help.

(_{Wish I'd drawn it now - it would've been quicker than all that explaining. Del, d'you still use that tablet thing? Haven't seen any offerings for a while})

It is remarkably simple to build a Switched mode PS with modern chips, I recently built a 10 amp programmable (for voltage output) power supply of this type designed by and published by the Elektor Magazine. Its uses two identical, easily obtainable chips and a handful of other components.....Worked immediately.....its easily programmed by a few resistor values.

The PCB comes from the company that supplies PCBs to Elektor, for the USA I believe there is another supplier. You also need a 10 amp output transformer of around 36 volts....so around 230 watts or better, either 110/36 or 230/36. A toroidal transformer would be best.....and physically smaller and lighter I believe as well as giving far lower emissions....

The chips are fully short circuit and over temperature safe.

For 10 amp output, a cooling fin is recommended and a tiny fan in a box with ventilation holes. The chips used can safely supply up to 40 odd volts.....A "bigger Brother" version can be programmed to supply up to 60 volts if needed.

The chips used can each supply up to 5 amps, which is why Elektor used two of them for 10 amps. The supply was originally designed for a HiFi system, so is of really high quality and has really low noise......

If anyone is interested, just send me your private email addresses via the CR4 mail system....and mention exactly what you need:- "The Elektor power supply .pdf."

Open SMPS and check out put Fast recovery diodes. If diodes voltage rating is more than 50V you can series without any problem. good luck!