Possible faulty power supply causing boot loop on 16” 2019 MacBook Pro

Hi I’ve just bought a A grade 2019 16”Macbook Pro. I’ve had problems with it since it arrived and te company I purchased it from are happy to take it back. When i turned it on it would boot to the Apple logo, shut down and then automatically repeat this 2 or 3 times. It would then come up to the log on screen. I would start to type the password and after say 3 digits it would freeze and then reboot again. Usually after going through this loop 5 or 6 times it would boot ok. I did as suggested and unplugged the power supply and tried again. It worked this time. I tried reboot about 20 times and it seemed fine. I then used it on battery for a full day and it was ok. I even tried shutting it down periodically and it was all ok. I then plugged in the charger and it faulted again. I changed the USB C TO USB C cable and it seemed to run ok on this until it was fully charged. Then it started again. If I shut it down normally with the cable plugged it’s ok for a minute or two and then it mysteriously reboots itself. This does not happen at all if I unplug it. I ran Apple diagnostics and no faults were found. Thursday ony thing I get after a boot loop is a message to say your computer restarted, because of a problem. That shows Kernel 1 panicked. I see neither the power supply or the cable are genuine Apple, and its they that are causing this problem. Can anybody confirm or help in any way

Ken