Here's a generic, cost-saving measure for those other people who like me are creative, somewhat technically inclined, cheap, and have an old/spare power-supply lying around, and would like their running power supply to have an 8-pin CPU connector, but it only has a 4-pin connector.
Disclaimer: use this info at your own risk. If you screw it up, that's because YOU screwed it up, not me
and also, this assumes you are not in danger of or concerned about voiding any warranty on your power supply (or any other component for that matter).
1 old spare power supply with a 20 or 24 pin motherboard plug
1 bobby pin (hair pin)
1 soldering iron & fine 60/40 or similar non-acid-core solder
1 X-acto knife, hacksaw, or steak knife type of cutting tool
1 nail file and/or sanding block with sandpaper
1 set of wire cutter/strippers (optional)
1 sewing needle or push-pin (optional but helpful)
SO, you take the old spare power supply, which has a 20 or 24 pin motherboard connector on it as usual, like this diagram tries to show, using @'s for the rounded connectors and #'s for the square connectors (this view is looking INTO the business-end of the power supplys 24 pin motherboard connector, with the locking clip on top):
If you are dealing with a 20 pin version, it will be the same, minus the last 2 pins on each row's right-hand end.
Now, the section we are interested in involves the 8 connectors under the locking clip, which are shown in some sort of RED COLOR
If you do the research, you will find that the shape and arrangement of this chunk of 8 connectors is identical to the shape and arrangement of the 8-pin CPU power connector you desire.
Take a hair-pin from your wife/girlfriend (a bobby-pin), open it to a 90' angle, and scrape the plastic junk off of one tip of it.
Insert the tip of the hair-pin down into the front of the connector block beside each of the 8 pins you are interested in, to disengage the 2 tiny metal tabs that are holding the wire pins into the connector block. The tiny metal tabs are 180' apart on each side of the metal pin, and take VERY little effort to disengage. With the 2 tabs of each pin disengaged, you should now be able to pop the metal pins out of the connector block by pulling the wire.
After you've removed the 8 wires in question, use a hack-saw or X-acto blade or similar small cutting device and chop off the remaining sections of the connector block to each side of the 8-pin chunk we want to keep. Chop just outside of the piece we are keeping. Using the X-acto knife (or a steak knife in my case) and a nail-file or sanding block, clean up and smooth the freshly chopped edges of your new connector so it's nicely squared and smooth. And presto -- a shiny new 8-pin CPU connector.
The old power supply has some other wires we want. Specifically, we want two more yellows and two blacks, with THE SAME TYPE of metal connector-pin as the ones inside the motherboard connector block (little square ones like from the 4-pin CPU connector, NOT the thick round hard-drive plug pins). Open up the old power supply and snip your choice of wires off somewhere within an inch or so of the circuit board, and gently pull them out of the unit. Strip 1/4 inch of insulation off the end you just snipped and twist the exposed wire so it's neatly twisted and pointy, and not all frayed looking. Repeat the hair-pin procedure to remove the pin-ends of your new wires from their plastic connector.
IMPORTANT: power supplys contain capacitors, which can hold a significant electrical charge for some time even after lying around unplugged. The capacitors in the supply are relatively small and the chance of hurting yourself is ridiculously remote, but there is the possibility of atleast startling yourself by accidentally shorting some metal object across a charged capacitors terminals. For this reason, unplug your computer from the wall, and press the power button several times as though turning it on. This will attempt to discharge the stored electricity from the power supplys circuitry.
Disconnect & remove the power supply from your computer case and plop it down on the dining room table where there's lots of room (this also excites the wife, assuming you're male or otherwise living with a woman who will be concerned about the finish on the table, which will add amusement for you).
Repeat the hair-pin procedure to remove the four wires from your power supplys 4-pin CPU connector, and (discard) place the connector off to the side somewhere, or in a spare-parts bin.
Remove the cover on the power supply. Remove the (4) screws that hold the circuit board down, and gently lift the circuit board out and station it such that you have comfortable access to both sides of the board in the area where all the wires attach to it, preferably with the solder-side to the hand with which you will use the soldering iron, which incidentally you should now plug in and warm up.
Notice on the bottom of the circuit board (the solder-side) the large areas of copper/solder where all the yellow wires pass through and are soldered to the board. Chances are extremely good that there are unused holes for our purpose, through which you will insert the end of each of your new freshly stripped and twisted yellow wires.
at this point, before soldering anything, be sure you thread your new wires through the big doughnut-shaped plastic grommet in the power supply's housing, or be sure the grommet comes apart so you can put your wires inside it with the rest of the wires.
Now, solder the copper wires onto the circuit board with the rest of the yellow wires, replicating the fine example your power supply manufacturer has so kindly set for you. Be sure your wire ends do not protrude out from the board's underside any further than the rest of the wires soldered about. If they're too long, they could short out against the housing, so snip the excess off, making sure the pieces you snip off do NOT end up inside the power supply.
Repeat this procedure to your two new black wires, soldering them into the pad alongside the rest of the black wires, hopefully again through some handy unused holes into the solder-pad.
Almost done! Reassamble the power supply gently. You now have 4 black and 4 yellow wires coming from the supply.
Using the push-pin or sewing needle, very gently, pry up the tiny locking-tabs on each metal connector pin on each wire, so they stick about 1/16 inch out from the connector pin's body. Do this for all 8 wires.
Now, grab your new 8-pin plastic connector block that you made earlier with the steak knife and nail-file. Your 4 yellow wires will go into the row of 4 holes NEAREST the locking clip of the plastic connector block. The 4 black wires go into the remaining 4 holes on the row FARTHEST from the locking clip. The pins will lock into place.
As the metal pins are square, you may think they can go in any one of 4 ways, however there is (generally) only ONE way they will insert -- notice the little pair of spurs sticking off the side of the connector pins; these 2 little spurs line up with 2 little slots inside the plastic block, which you can see by peering down into the holes on the back-side of the plastic connector block. It varies by manufacturer as to which side the slots/spurs are on, but if your eyes are bad, or it's dark where you are working, or you just plain don't have any spurs and slots, gently try inserting the pins into the block each of 4 ways. They'll go in eventually.
All done! Reinstall the supply into your machine, reconnect everything, and enjoy your new 8-pin "ATX12" or whatever it's called