Thank you Tobias, I'll wait for the new PSU to arrive and then go from there
I'm now running an ACA 500 with a 1221EC accelerator. I recently replaced my original PSU with the icomp CA-PSU and it solved all my stability problems. I also recommend the acrylic case from plexilaser.de to keep everything safe (and neatly route an ECSv2 VGA cable if you have one of those).
If you do get a case it's best not to place the CA-PSU on top of it. I absent mindlessly did that blocking the air holes and radiatated heat into the plexi case - it didn't crash but it did feel warmer than usual so I won't do it again 
