I am not happy with both the Power Supply 20 to 24 pin motherboard cables, and the 24 to 20 pin cables. They are so cheaply made, and have run into some that have intermittent connections because of crap quality. The company these come from seem to be Startech. When I buy a cable from Frys Electronics or Newegg.com the only ones I can find for this purpose are from that company.
6in 20 Pin Motherboard to 24 Pin ATX Power Adapter
StarTech.com ID: ATX2024FM
And, I have to let you guys know, the quality is aweful. The quality of the pins and the workmanship is bad. This causes intermittent power conections. I know that these cost pennies to make, yet people like me buy them in a store or online and pay $7.00 or more for a crucial product that connects a computer power supply to the motherboard. Then, to have an intermittent power connection not only causes grief with the computer not working properly, but also causes it to destroy parts whent he power is intermittent.
Furthermore, your company seems to be the only one that has these cables available in stores for this purpose. So, we do not have another choice.
I hope you will fix your quality assurance, as you are surely making more than 500% profit from this one part alone.
Please take my advise as when people complain about a product on the Internet, as I do, others will read the company name and the complaints about them and avoid their products.
Considering you can get ones from rosewill or apevia for under $5 i dont think the price jump to the startech ones was worth it, its a simple power cable, on something that simple you are just paying more, not buying higher quality.
For that matter, you do not need an adapter. The extra 4 wires are one each 12 volt, 5 volt, 3.3 volt, and ground for the increased current demands of later (but not the newer) motherboards. So the adapter will not increase the power available from the PSU.
Just plug the 20 pin connector into the appropriate motherboard connector pins. If the PSU has adequate capacity, it will work. If the PSU doesn't, the adapter will not make any difference.