I am thinking about adding new video board to my computer, a power hog of a video card and I know the present PS in the computer won't be able to carry the load. I have other PS's, none with enough power to power the load. Here's my question: could I add the second PS, both are for ATX motherboards, by doing a lot of cutting wires and soldering, so that both PS's would be connected to the motherboard, in parallel. I realize that the real answer would be to buy a more powerfull PS, but it would't physicaly fit in the space that the present (low power) PS. Would it be like connecting two battery's in parallel (no problem) or would the two PS's "fight" to maintain their voltage "set points"?
the first psu had 20 pin atx cable, the second has 24-pin, and that 4 pin could separate and connect on the 4-pin slot which was left empty because first psu only had 20-pins, that way when i power up the pc both power supplys started to work
There's no way the secondary psu would start just by hooking up the 4 pin, unless the proper pins on the main connectors were jumped, and then feeding the MB from 2 completely different source's was no-no right off the bat.
To more directly answer your question
Your question " Would it be like connecting two batterys in parallel (no problem)" Ans: No it is not the same, You can connect two batteries in Parallel as long as they have the same voltage (ie 12.6 volts for car Batterys. When you do this, if one battery is low say 12.2 volts, the 12.6 volt battery will charge the first and Eout will be equal. The current during this time is Very high. You NEVER paralell electronic PSs and it is for this same reason, if the voltage for one is slighlty >< the other, then one PS will either be a load or a source to the other psu. Almost similar to putting two AA batterys (1 a Nicad 1.25 V, and the Other a normal 1.55V) in parallel - end up with two bad batteries.
Can you use two PSUs in the same compute? Ans Yes. But you must insure that the circuits are isolated from one another. Ex. PSU1 +12 V to all Molex and PS2 to all pcI-e +12 V connectors = OK. Psu1 4 pin atx conector to !/2 of 8 Pin atx mb connector, Psu2 4 pin atx power to other half or if you have a GPU with 2 PCIe connectors and you connect PSU1 to one and PSU2 to the other= no-no.