I had always read each pcie cable could support 150 watts each which is why the current gen 3080s use 3 cables. Though these new 16 pin versions somehow can support up to 300w on a single cable. Not sure why though.
Jonnyguru (formerly a very popular PSU reviewer and now head of power supply R&D at Corsair) clears it up in this video:
The short answer is the PCIe cable rating was made for the connectors on the PCIe (not power supply) end in a time when GPUs consumed significantly less power.
EPS 8 pin (CPU) cables have always been able to carry 300W, despite using the same connector on the power supply end as the PCIe connectors.
Jonny's site also has a bunch of common PSU issues broken down:
http://jongerow.com/Common_issues/.
Finally, there's a few Discords servers with people that have a lot of PSU knowledge, i.e. Cultists Network and Hardware Busters (Aris' servers, the person behind Cybenetics who do very good power supply testing, they also have a public database with lots of testing data on efficiency, noise, protection etc.).