RX 480 Computer restarts when playing.

Make and model of psu, specifically?

Tried running DDU and reinstalling fresh drivers?

It could be lots of things, the most likely culprits are:

power - i googled your PSU but the results came out inconclusive, first make sure your PSU is at minimum bronze rated, preferribly better. even if it is, 500w for your set-up may not be enough under load depending on the rest of your peripherals such as HDDs, SSDs, anything else.

also check your windows power options, make sure you have everything set to high performance, not balanced or power saving.

your mobo drivers and BIOS. make sure you have latest of both, especially the BIOS.

try a different PCIE slot, the GPU should be located closest possible to the CPU, but you can try a different slot, dust it off before you do so.

overheating, even though your wattman is reporting everything is ok, doesn't actually mean that it is. your cpu may be overheating during heavy loads or even the PCIE port itself, or your main RAM.

after you update your mobo BIOS, go and disable any "SMART" fan / cooling functions. they are misleading and do not work well, especially with systems that use lower rpm quiet fans, I don't know what the equivalent of these functions is called on the MSI boards, but on Gigabyte boards its "SMART fan control", and nearly all mobos have them nowadays. but it causes issues because basically the mobo will expect a certain RPM per certain temp, but it won't get that range because of the different fans working differently and it will shut down your components and or in some cases entire computer when this happens.

make sure that in windows power options your HDDs / SSDs are set to NEVER power off or sleep (at least the ones for your main OS and games)

go into mobo BIOS, and disable any PCIE port overclocks and/or voltage adjustments, the rx 480s have enough PCIE voltage problems on their own and I just can't imagine any additional drama from these would be good for it.

disbale all memory and CPU overclocks, these can cause some major issues, as well as hog even more power on your already very possibly inadequate PSU.

in the AMD driver suite, reset all global settings to factory defaults, save and reboot your comp, uninstall and reinstall drivers again, BUT this time do a full clean uninstall. to do that do the following:
1. go to safe mode without networking - this enables much more control and better uninstall then regular
2. uninstall regular like always, then do a search on your computer for any leftover files from catalyst, amd, radeon, dump them all, EXCEPT windows system files and your CPU drivers etc.
3. use CCleaner and dump all bad registry entries as well as clean all the temp data on your machine.
4. shut down your computer and wait 15-30 secs, then power back on and log into default windows.
5. re-download the driver package
6. do a CUSTOM install, do NOT install expres
7. in custom, unselect the "Gaming Evolved" thing, it is known to cause drama for many people on many systems and supposedly they are still working on patches for it.
8. do install the vulkan API, for some reason many games and AMD suite itself uses its components, even if their not supposed to, so its abscence also causes drama.

there were also some main memory management issues caused in games by windows 10, but unfortunately I do not remember the specifics, this is applicable for the previous as well as the new patched builds. I do know that my full modded with ENBs and around 200 mods skyrim runs far better on win 7 64 bit then it does on win 10 64 bit. win 10 has a lot of stutter and the game crashes frequently, whereas i can get around 2 hours of playtime before i crash on win 7.

hope some of this helps