My brother has just been given a HIS ATI Radeon HD 3850 card. He has a fairly old PSU without 6 pin PSU connectors on it and I though i just needed a 4-pin Molex to 6-pin PCI-E cable/adaptor to power the card.
However on the one i bought the head for the PCI-E end does not fit. There appear to be 3 'rounded' pins and 3 'square' pins on the cable/adaptor but 4 'rounded' pins and 2 'square' sockets on the cards power socket. I'm wondering if i've been sold a 6 pin PSU to 4 pin Molex adaptor instead of a 4 pin Molex to 6 pin PCI-E?
I may be being really dense here so please let me down gently if I am.
If you need more info I can provide more but not sure what else you'd need to know.
I think you bought the wrong adapter. And I was surprised to notice the HIS HD 3850 card didnt include a power adapter cable in the accessory pack. The picture below is the accessory pack for the Asus HD 3850.
You can see the power cable with its black PCI-e header and two 4-pin molex connectors.
A close up of a PCI-e power adapter cable:
I could not find any 3 round / 3 square 6 pin cable in the short google search I did.