Hello guys, I wasn't able to find this online, maybe because I don't know how to phrase it in english in something that makes sense in a search, idk 
Thanks in advance for your time.
 
So to make things short I seem to have lost one of my PSU cables... f
The PSU is the EVGA 550 G3 Supernova. It must have had 2 PCI-e cables, since it has 2 slots. But now I only have got one cable that says "EVGA" and "VGA G3". I've got another one that I assume is from another PSU, it looks high quality enough, it has the 2x 6+2pin on the other side.
It won't fit the PSU though, one of the pins on the cable has the square plastic and the hole in the PSU is the rounded one. It fits if I force a little (did it without realising it was different, I thought they were all the same).
The change is because I'm switching graphics cards.
The thing is, will it explode if I turn it on with the "wrong" cable? Is this a special evga cable or where can I get it?

Some pics to make it easier:
Correct cable that was in use

 
"Wrong" cable:

 
"Wrong" cable connector:

 
PSU slot:

 
It won't fit because of the upper right .. "pin slot"? The plastic on the cable is square.
 
I'm a little lost here, so I appreciate any help!!

I would call EVGA and see if they can send you out a new cable.
They are pretty good about that. Make sure you register the PSU before you call or summit a ticket.
 

If it don't fit then it's not supposed to and the power and ground pinout is almost certainly different and could cause component damage.
 
The only way to know for sure is to check with a voltmeter..You can buy an el cheapo like this one at Walmart or just about any auto parts store that will do the job..You can remove and rearrange the terminals on the GPU-end as necessary according to the correct pinout..Sense terminals are ground..Component-end pinout is industry-standard while the PSU-end pinout can be different because there's no industry-standard there and that's the problem..Pinout diagrams are shown as if you are looking into the end of the connector, unless otherwise specified.
 
You can buy the correct cable here or here from EVGA or Contact EVGA about getting the 2x 6+2pin cable.