Hello.
I noticed that my power supply is a little hot while the computer is turned off.
Is it something normal or I should replace it?
Thanks!

Warm can be normal even when off. Modern PSU/motherboard combinations are "on" even when off and always drawing some power. Very hot/can't hold your hand on it is abnormal either on or off. Check too that the PSU fan is turning when computer is on. Fan failure is a common PSU malady.