The english in this thread is a bit confusing, so I will just make some statements and if they're not totally on topic I apologize.
First, it is very easy to set something like this up, there are even cheap little buttons you can buy for like $5 to basically be an on switch for both PSUs.
Here is one of the eaiest guides I've seen on the subject: http://www.overclock.net/power-supplies/14455-multiple-power-supply-guide.html
Now with that said my suggestion is: Don't do this
. It can have some problems which are obvious and ones which aren't so obvious (like imbalanced grounding). This is just a suggestion of course.
I am running 2 5870s and a 5850 on a single x650, and my power meter reads off their consumption for the entire system at 550W. I don't suppose 3 5830s uses more power than that, so I would be comfortable in recommending a 650Watt power supply as enough for 3 5830s (assuming you downclock the memory and use an efficient and small CPU like me, I am using a 45W sempron). An antec Earthwatts 650 can be had for $65 last I checked. That's pretty reasonable for a good PSU.