I used a HP PSU for my display last year and got a breakout board for it. Problem is the pinout was slight off, despite it saying it was supported. My PSU is 800watt. I believe the 750 and 1200's are the same but my dumb luck had a slightly different layout. I tried hacking the board but gave up and just soldered wires directly onto the edge connector, which worked fine.
Breakout boards may make things look neat but I am considering not bothering when I expand things this year. The large gauge wire is terminated with crimp connectors and runs into an 80 amp breaker then on to the fuse block. Still easy to swap out, just not as pretty.
There are quite a few pinouts by the look across the range of HP PSUs but there seems to be a popular one that many conform to. Problem is the specific one I got is only a little bit different to the common standard so it looked like it should work but didn't. Mine runs at 12.3, never thought about dialing it down and it ran the show without any issue with any pixels. By the time the wire ran any length the volts dropped a bit anyway so don't think any pixels saw anything over 12.