Compatibility of Optiplex 9020/7020, RX 570, and CX450M & Adapter

[blitzer]

Hello everyone, I'm planning to make a build out of an Optiplex 9020/7020, but have just gotten a bit confused as to compatibility between these components and hope someone can straighten me out.

 

CX450M & Adapter -

I understand I'll need at 12 to 8 pin (Dell specific) adapter for the new PSU to work. I believe this [ https://www.moddiy.com/products/Dell-OptiPlex-9020-PSU-Main-Power-24%252dPin-to-8%252dPin-Adapter-Cable-%2830cm%29.html ] is known to work reliably (unlike others where users note poor quality control), though I don't know what to do with the 1(?) pin molex connector - not sure what plugs into that.

 

CX450M & RX 570 -

I've seen it posted that 'many' power supplies that while in theory provide enough wattage, won't work with the Dell specific power setup because they don't provide enough power on the correct rails (3.3/5v) as seen here [ https://www.dell.com/community/Optiplex-Desktops/9020-MT-Problems-Installing-GTX1060-or-Radeon-RX570-oc/td-p/7277156 ] (search for "BARE Minimum working" and read that post)?

 

So, I've gotten a bit spun around and need some clarification - thank you for reading, any response is appreciated.