I would reinstall the drivers, you don't need to use DDU again, just download the application from Nvidia.co.uk and run it.
This won't fix what is going on the the PSU though. Make sure that the intake vent for the PSU is not obstructed ( the intake for your PSU is inside your computer, not at the back ), or filled with dust. Try cleaning it out with something like a can of air. But do NOT open the PSU casing to try to give it a better clean, there are capacitors in there that hold a huge amount of charge, even when the unit is unplugged. If these discharge on you the outcome isn't great.