Determine where the psu is intended to fit.
Bottom mounted psu on carpet.
Being placed at the top of the case a power supply could.
Extra cables are easier to manage as they lay on the bottom.
Avoid placing case on carpet for bottom mounted psu with fan down never put your computer case on the carpet when you have a bottom mounted psu fan facing downwards.
This is typically at the bottom of the case in most modern chassis designs.
A top mounted psu is like a 2nd exhaust fan but if you want it to run cooler go with a bottom mounted psu.
My psu is mounted in the bottom of my case a tj07.
The carpet will block the airflow to the psu and in worst cases if you have no psu fan filter installed then the small fiber particles from the carpet can get deposited inside.
Psu s mounted on the top have to draw air from inside the case.
When intel designed the atx form factor the power supply fan was designated as the primary case fan.
My computer sits on my desk and imo i would never set a computer on carpet.
Mounting a psu in the top of the case should be ok as long as it vents to the top.
This means that they will run a bit hotter than a psu that is mounted on the bottom which draws air from outside the case.
The problem of bottom mounted power.
To figure out whether your psu fan needs to point up or down start by looking over your pc case.
Hot air rises and cool air you get the point.
You have to have space under the case though and be careful on high carpet.
On a correctly oriented bottom psu it pulls cool air from the bottom and blows out the back.
Deciding on whether to mount your psu either facing up or down depends entirely on a few factors namely case design airflow with other fans and the power supply unit itself.