Hi Steve, To answer your question, the PSU does not have any control of the fan speed on load or temperature. 
I've just bought (from ebay) a T320 with a non redundant 350w PSU and the PSU fan is very noisy as if it has no thermal control and is just set to max speed. This is not "it's failing" noise, it's just "it's running at high rpm" noise. The rest of the box looks fine and seems to work fine. The fan is certainly much louder than my T320s with dual 495w redundant PSUs when they are idling along ... and I think it's noticeably louder than when they are working at a normal level. The system board fan is fine... spins up when expected... drops down to a low speed/noise when expected ... so no problem there that I can see. Bios settings are performance per watt but don't seem to make a difference and I disabled C1E at one stage as I'd seen a comment about that somewhere. I've run it up through LCC and also to the installed OS and left it running for 30 minutes and no change at all. I've also run it up without disks (it has 4 x 1TB SATA disks installed on S110) The plan was to buy a box for non-critical low load test office work that would be nice and quiet, so maybe I've made a mistake. The person I bought it from said that the fan had always been that way. So the question is... what should I expect ... is it expected that the PSU fan will always run at full speed whatever the loading ... or should the PSU fan speed be related to load/temperature. TIA for your time and any comments Steve  
T320 high fan speed, noisy non redundant power supply