Could be a factory faulted item. I also did a PSU change of a PS4 slim and played for an hour and shut it off. The next day I played for an hour again and shut it off then tried turning it back on did the same PSU faulty symptoms (beep turn on and shut off instantly). Weird part about mine though is that if I turn it on then off again (disconnect from power point) and do a system discharge by holding the power button, the console would beep once with no lighting turning on. This I did not experience with any other console I discharged after turning off power. Could be something to do with a faulty capacitor or something since that’s the dude that stores the charge. Also, I had ordered two same PSUs and the other PSU worked fine but this one had a really short life.