Consider a power supply to be a two teminal battery. It has a + and - Output. It can be wired in series to ANY other DC power supply (even different voltage, different max current) AS long as the - output is NOT connected to the chassis ground. You wire them like batteries in series + to - and the outputs from the ends. [( - + - +) A lot of cheap computer supplies have their ground tied to chassis and AC safety ground via the AC Cord so they won't work without modification but commercial switching supplies (like the ones I listed) do not assume you want - to be earth ground.
The AC side gets tied in parallel and the + and - output terminals tied in series. Each supply regulates it's part of the voltage so in theory you can hang different voltages in series and each supply regulates the voltage across it's terminals.
Since the same current (total circuit current) flows across all series components each supply has to supply the same amount of current. If you mix supplies as to current capability the max current is the smallest number in the string.
It's just not that difficult. Even if you hook them up wrong ( - + + - ) all that happens is you get the difference rather than the sum (essentially zero volts if they are the same). Nothing blows up. Just no current flow.
Now, running two regulated supplies in PARALLEL to get double the CURRENT is NOT easy and requires that the power supplies have special Master and Slave current sharing circuitry. They have to be very close to each other as to output voltage. Otherwise one will always take all the load. You can diode isolate each one and or use series "balance" resistors but it eats up power and is less than truely balanced.
There is a lot of FUD about power supplies and how to size them and what kind is best and what you can and cannot do. Thing is, that magnetics and power conversion is the heavy lifting part of electronics and runs under it's own set of physics and rules. Someone posts something as fact, it gets quoted (sometimes incompletely) and turns into "rules".
TOM Caudle
www.CandCNC.com