think cooling is very required to control the humidity of psu......
Stepping 120V(or 240v in other parts of the world) down to 12v is always going to generate some waste heat.
While PSU have gone from 70% to 92% efficiency in the last 15 or so years, the components inside are still heat sensitive.
Excessive thermal build up will destroy, and the higher the temperature, the faster the destruction in a non-linear acceleration.
Even the highest quality capacitors are only rated for 50C use.
So, the answer to your question is that cooling is required, and a fan is still the simplest and cheapest method.
PS...you ever wonder why Apple products are sealed and cannot have the battery replaced?
When you make things insanely thin and without fans, they are going to fail.
Making everything fail at about the same time makes sense to keep the consumer addicted.
After2, 3 years, your warranty is gone, your battery is dead, and the thermal load most likely has worn everything out so that attempting to replace the battery is pointless anyway...
Time to buy the latest and greatest Right?
Thank goodness they planned this out to give you the justification to upgrade without guilt.
Just FYI, my calculator, HP15, form 1982 still works.