I only tried to separate the AC heater as far as possible using the empty pins for spaces on the umbilical cord and as far away from other wires as well
for the PSU cable wirings, I twisted the AC heater together with ground wire and the other wires twisted in pairs, and cover them in a braided shielding and a sleeve. You can also overkill this by using a huge aquarium hoses and cover these 3 to create spacer away from the rest of the bunch. I don't care for a flexible PsU cables, just as long as it work great. I did not use the hose though
The main hum problems should be from the main AC that may get too close to other wires, especially input-output. Just as long as you manage to keep them away from those, you should be safe. That is just my experiences