Psu s mounted on the top have to draw air from inside the case.
Bottom mounted psu on carpet.
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.
Determine where the psu is intended to fit.
Extra cables are easier to manage as they lay on the bottom.
Once you ve located where the psu will sit check the case for any grills or vents directly beneath this location.
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.
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.
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.
In my case i get cool air for the intake and the hot air goes out the side of the case.
This is typically at the bottom of the case in most modern chassis designs.
To figure out whether your psu fan needs to point up or down start by looking over your pc case.
Being placed at the top of the case a power supply could.
My psu is mounted in the bottom of my case a tj07.
You have to have space under the case though and be careful on high carpet.
A bottom mounted psu keeps the psu cooler not the case.
The problem of bottom mounted power.
Hot air rises and cool air you get the point.
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.