Thanks! Yeah, the fan header in the sf750 is different. I got a 4-pin mini-GPU fan head to regular 4-pin PWM adapter and had to re-pin the adapter NOT the noctua fan header.

• Amazon Link
• Reference user der_brennesel's post on Feb 9, 2021.
  • https://smallformfactor.net/forum/threads/corsair-sf-80-platinum-fan-mod-swap.12251/post-238892
• Re-pinned exactly as shown in the post and that did the trick.
  • Verified psu fan spin up during pc start-up and if psu fan was working while under heavy load. Stock fan is usually off during idle.