Did you remove all of the old drivers before you installed the new RX480?
(if not, use DDU in safe mode to remove all old drivers)
Windows power plan needs to be set to "Performance".
Turn off all power savings features.
Your PSU should be fine, it has 49amps, but you may want to check it to be sure.
I removed old drivers with DDU and installed different versions of drivers
I haven't tried out the permormance profile but I remember setting it up in permormance a while ago, I'll check it out anyways
I don't think it's a malfunction of the PSU because I tried it out in another system and I had the same issue
Power options is not the issue, I changed it to be focused on performance and it has the same issue
If you can, try the GPU in another computer, if you get the same results the card is going bad.