Are PCI-E connectors universal?

I sold my GTX 770 recently. The buyer asked if I had a 6+6 pin to 8pin adapter because he only had 6 pins and no 8pins. There was one included when I bought it. He now wants a refund because he says the 8pin doesn't fit in the card which I really doubt since it was included. What should I do?
Isn't the pin layout the same with every GPU?
Should I refund him anyway? He passed the 14day return window.

well isnt your buyer confusing with the cpu 8 pin connector?
Cause the 8 pin cpu power, does not fit into a gpu.

But pci-e connectors are universal, so a dual 6 pin to 8 pin adapter should fit.

Also a psu that has no single 8 +6 pin pci-e power connectors now days, sounds realy rare to me?
Unless its a realy low wattage one....

If he has such a shitty psu that it doesnt come with 6+2 pin pcie cables he shouldnt be running a 770 anyway.

I second what @MisteryAngel said.
From a legal standpoint, depending what country you are in of course. But in the UK and USA The law is very much in the side of the seller for second hand sales. Unless you misslabled your product or out right lied to him you don't legally owe him a refund.

As above; incompatibilities are not the fault of the seller. 8-pin and 6+2 pin PCI-E connectors are indeed universal for graphics cards (and 6-pin for a 6-pin port).

Coincidentally, MrBlame, you are not to blame.

I will try asking him.
I don't know of his PSU but I couldn't really care less. I already told him he would take a risk using it when his PSU didn't have a sing 8 pin.

I told him but he bought it anyways.

First time selling on eBay so good to know :)

Good. I won't refund him then :)

That just made my day :)