Hmm, this reminds me. I have a FSP Group 500 Watt PSU. It's about 5 or 6 years old, the best PSU I've owned. But I wonder if that's my issue? I know the fan inside of it is basically shot, it's so loud right now it's unbelievable (I ordered a new fan). So I'm wondering if maybe the fan is making my PSU hotter and the voltage is decreasing? Or I simply don't have the power to run this many harddrives? I mean, technically, only two of them were connected. The other one is a external USB.
But now I have three, I ran OpenSuse and didn't have any issues like that.
Normal fan can be used for about 2-3 yrs only. So problem should come from the fan not the SMPS i guess... What is the model you were using?