Hi, there is a little bit of info missing here but I am going to take a stab in the dark...
I assume you are paralleling 3 switchmode power supplies together ?
If so, even though they are rated at 48 Vdc output there will most likely be a small voltage difference between them, in fact most switchmode's I have seen have a voltage adjustment on them implying they may not be EXACTLY the rated output. So what may be happening is that one or two are fighting each other as far as the output voltage is concerned, so most likely the one that is set at a slightly lower voltage is trying to push the voltage level up and smoking up as a result.
So what to do to fix the problem...well I don't know what you are powering from this setup, but my guess is a 3 axis cnc machine of some sort (this IS CncZone after all )
If this is the case then you could power each individual axis with its own power supply and not join them together in any way, so you don't have to change power supplies and waste any more money.
Now before you go ahead and do this you should maybe let us know what exactly you need from this setup so we can make sure we are giving you the right information, as you could also possibly introduce more problems by splitting up the supplies. Generally grounding will be the "introduced" problem, but with some careful wiring this can be avoided.
Hope this helps.