HELP Computer shuts down / hard chrash

[StAndrew]

I've been using the VisionTek Juice Box VT-450CD 450W for 10 yrs.
Made by FSP works great.Paid $100 brand new ,I believe its 85%@ 300w
Powered sli 285's & 580's
Main psu is corsair HX650

Ha! I just bought a FSP BoosterX 300watt. I'm running it to two 6 pins on two cards so it should only be running at ~150W. GPU's are now running at 1226 and I think I have more head room; going slowly. Before, 1213 core artifacted and shut down. 1200 just shut down. So it definately was a power issue.

But it doesn't make any sense at all.

The maximum watts I'm meausring at the wall is about 1020W, with average around 950 - 970 watts. Assuming ~%90 efficiency (the Seasonic is Platinum rated IIRC) this means the peak load on the PSU is ~920ish watts. 1200 should be plenty. And this is calculated with the FSP 300W boosterX (uses the same power strip) which would incure even more power loss in efficiency so peak load requirements are probably a few watts lower.

Is my PSU bad? I have plenty of case circulation and CPU/GPU's are watercooled

I know back in the day some PSU's were unable to completely load the 12V rail without a large enough load on the 5V and/or 3V rail... Is that still an issue? Only running two SSD's.