Help selecting a power cord.

What are you using to plug-in your gear? Power strip or Conditioner?
I recommend Zavfino Majestic MKII ($324-1.5M) power cords in following order,

https://zavfinousa.com/collections/power-cables/products/the-majestic-occ-power-cable-12awg

Tube Main
Tube pre
D/A
CD transport
Turntable
Subs (last)
Roon Nucleus uses DC cable, I suggest you upgrade its stock power supply to a linear power supply.

You asked, “So if you could only do 1 upgrade, would you do cords, or power conditioning??”

Power Conditioner like Audience Forte, it comes with a very nice power cord,
https://audience-av.com/conditioners/forte-power/

If I was going to try just one pc I would choose Cullen. Those seem to make a positive difference wherever they are connected. Then move it to a different component every few days and decide where it fits best.We all gotta start somewhere.

Take a serious look at the Puritan power conditioners, 136 and 156.  Less expensive than the big boys and actually more effective.  If I had to apportion money, I'd put it there before trying power cords.  BTW, the Puritan PCs are also very good and don't break the bank.  But the 156 is transformative: check out several threads about it here.

Use Pangea Audio cables on everything for power cords. I did everything at once so I can’t comment on where to start. They have different cords depending on the component type.

I wouldn’t beak the bank on power cords. For me, they didn’t make much of a difference. Power regeneration did make a big difference. I use PS Audio P20. They have smaller units to fit your budget and needs. They also have a 30 day return.

Agree with Chayro