dead A1082 23 inch Cinema Display DVI monitor

I have a similar issue with a dead A1082 23 inch Cinema Display DVI monitor which I use as a second screen to a 2014 iMac 5K.

First I thought it was a faulty PSU but swapping it for a different power brick (I knew was ok) did not help. It also failed!

Swapping the power brick back to power another 23 Cinema Display DVI (that I also knew worked), also failed to boot.

So I had a good monitor, a good power supply that wouldn't boot up as it should. Ether the PSU had just died, the monitor had just failed or something else was going on.

Leaving alone for a while, I returned to try and see if the original power supply would work with my good (now non-working) monitor and it did!, everything booted up fine. However, further testing revealed both power bricks were okay too and using the power supply I initially thought was faulty enabled my good monitor also to boot up fine.

So, I still have 1 dead monitor, but it's not the power bricks that are the problem unless they are both dodgy, this seems unlikely.

Just wanted to add the above to say the PSUs seem to power up if they start from cold, if warm they don't seem to power my second monitor and the screen remains black