Was wondering if

[HadEbola]

If I put my gpu power cord into my cpu header could that fry my motherboard or other parts?

[Guest]

Yes. Don't do it.

[Tan3l6]

It should not be physically possible. But don't try it with excessive force either.

https://superuser.com/questions/849265/is-there-a-difference-between-8-pin-eps12v-and-pci-e-connectors/1297931

[HadEbola]

Is it 100 percent guaranteed to be ruined? 
because I have done just this unfortunately as none of the wires on this PSU have indicators of what goes where:( 

Am currently waiting to be able to test a new PSU in hopes of a miracle.

my gpu and ram still work though I tried them in a friends computer so is there hope? Or is my mobo and cpu done for?