@charles1dad thanks for the reply, although not a very good news for me.
I will do a test, I wonder if it is because of the PS Audio Power Plant. My set up is this:
wall outlet -> BPT 3.5 -> PS Audio PPP -> my equipment.
my PPP also remains on all the time. So, I wonder if the PPP is drawing power that make it so hot …. The output voltage of the BPT is ok, stable at 121V. There is also no smell or hum. Music also sounds good from it. so, everything seems working properly except it is very hot.