Same nightmares with RX5700 on 4k. Changed HDMI cables, PSU, update Bios, reinstall drivers, win10... doesn't help... many users on reddits have the same intermittent issues... swap in a Nvidia all normal ;-)
Didn't bother to RMA, undervolt and use it for MS office, no more AMD Radeon...
LOL
No problems with my Sapphire Tri-X Radeon™ R9 FURY 4G and SAPPHIRE NITRO+ Radeon™ RX Vega64 and all previous Radeon cards (since Radeon 32)whatsoever, NEVER undervolt in my life before as well...
Know which drivers version best for the GPU
Know how to troubleshoot
NEW Adrenalin 2020 GUI got problems... NOT the drivers
Users solved the problems by installing Adrenalin 2019 19.12.1 GUI/UI (but upgrade to) with Adrenalin 2020 20.2.2 Drivers
LASTLY, TS focus on your suspected PSU issue, don't get DISTRACTED