I have a problem with the power supply temperature on two older iMacs (iMac7,1 according to EveryMac.com) running extremely hot on Debian 10.
This means that the PSU temp reaches 80°C+ after an hour or two of idling as reported by lm-sensors with applesmc-isa-0300 module (sensor Tp0P).
I'm specifically mentioning this because I'm not sure how accurate the readings are. The GPU temp shows a value of ~10-15°C usually. However, it is a Radeon GPU and I know that the temperature readings of AMD devices can be a bit wonky with non-AMD tools. So maybe the readings for the PSU are also off.
The case gets very hot to the touch after a few hours of idling but that doesn't necessarily mean that the readings are accurate. However, the heat seems to be emanating mostly from the general area where the PSU is located under the case.
Both machines are the same model (iMac "Core 2 Duo" 2.0 20-Inch or iMac7,1), both are running Debian 10. I already cleaned them to make sure that there is no dust clogging up the fans or the gills of the heatsink or any other paths that might inhibit the airflow but, as far as I could tell, it didn't make any difference. Maybe a .5 degree difference but generally too little of an effect to actually notice if any at all.
I managed to drop the temperature on both of them to about ~70°C with the aid of macfanctld running the main fan (which cools the GPU, CPU and also the PSU) at max speed of 3500 RPM. However, this seems still way to hot to me, especially with the fan running at max.
I also tried to use powertop to improve the general power management of the device by applying all the recommended settings, hoping to drop a few degrees in the process but that also made no noticeable difference.
Another distro I tried was Manjaro 18.10, but with the same results. Maybe running a vanilla Mac OS X on the machine might be worth a shot to see if the PSU is running cooler on that. However, I didn't receive any install media with these machines. So, I can't test it right now.
I'm kinda out of ideas at this point, hoping you can give me some advice on what to check or test, so that I can hopefully fix this problem.