My PSU and GPU were purchased at the same time (Around 2013- GPU had been RMA-ed once in 2014,but I am not sure about the exact year of GPU RMA.). As far as I remember about the PSU issue. the sequence of events were:
1) My GPU started giving Memory errors in HWinfo but I ignored them for a while since it was , at that time , not giving slower framerates for the games I was playing.
2) Then,my PC would not boot if I tried to turn it on after ,say overnight,but after a couple of tries,it booted up and after that it used to boot up normally within the day.
3) One day, the PC would not give any display.The fans would spin and lights would light up ,but before it could boot to windows, it shut down. After that, it refused to boot.That's when I took it took to Nehru Place for checking and the engineer there confirmed it was the PSU (After checking with a spare PSU). After replacing the PSU ,the PC worked okay for some time but then the issue I highlighted in my thread (Desktop boots without display or turns off occasionally.) cropped up.Please keep in mind I had been using an RMAed GPU for close to 4-5 years.
4)In around June this year,my RMAed GPU finally died with RSOD and I had to replace it.
So,roughly the GPU (June 2019) died after a year after the PSU (August 2018) was changed.
Also, yes, the system would restart unexpectedly in the middle of some games and around that time, the PSU was already pushing 4+ years.