I have an old power supply (Thermaltake TR2 420w) that works fine, however it has a weird issue where it turns on by iself! At first I thought hte issue was with the computer it was connected to, but with the PSU sitting on the bench with nothing connected, when i plug the power cable in the fan starts to spin and it's delivering power,

Has anyone seen this before? Any ideas how i can fix it? Basically any PC I use it in cant be turned off properly, which is really strange.