Point taken. See the update of the first post.
Another point which I think should be mentioned here is that one can have the best of both worlds.
A number of high end PSUs allow for you to use it in fanless mode up to a certain thermal limit above which the fan will start to kick in at low RPMs and gradually increasing when the PSU is under load.
So what is the advantage? In a word - price. You pay a premium for a completely fanless PSU and it is not negligible. An example in the UK would be:
Super Flower Leadex Platinum 550W £81 (hybrid or eco mode fan)
Seasonic SS-520FL2 520W Platinum £125 (fanless)
(I chose the prices from a single vendor which sells both of these PSUs)
The two PSUs are very comparable from the build quality - probably about as good as it gets - so I am comparing like with like.
Realistically the Super Flower could run at 250 Watt output continuously without the fan ever engaging. At 250 Watts the PSU is also in its sweet spot with regard to efficiency (50% rated wattage +/- 6%)
Another thing to remember is that in the UK where we use 240V the same PSU is more efficient than in the US where the mains supply is 110V at peak efficiency (50% load) it will be around 2% more efficient which of course also means less waste heat.
A PSU with fan that only spins up when needed gives one a greater choice with regard to cases than a purely fanless PSU.