I’m looking for the PCI-Express 6+2 pin, and 6 pin cables for a PowerBird 1100W PSU.  I’ve tried several after market cables, but they will not work. If you can point me in the right direction as to what type and brand will work best or even the original set that came with this PSU would be great.  Need and extra set for an SLI setup with 2 EVGA GTX 770 GPU’s.  Thanks.

Well, it's in an HP Blackbird and would take a lot of rewiring for a new PSU (which I'll probably have to do eventually.) 

Funcle
I’ve tried several after market cables, but they will not work.

Why not?

If the connectors are keyed wrong you can round the corners off the square pins with a sharp/razor knife like a utility or X-Acto knife so they fit.

If the electrical pinout is wrong, you can fairly easily remove and rearrange the terminals..You can buy an el cheapo digital multimeter for $10 or so that will do the job for checking power and ground.

Either way, make sure the component-end pinout is correct..The 6-pin and 8-pin (or 6+2) pinout here is shown as if you're looking into the end of the component/GPU-end connectors.

Funcle
The connectors all fit correctly, but it must be a power/ground issue.

If that's the issue then I would just rearrange the terminals as necessary, not hard to do..Go by the pinout diagram in my previous post.