Mac Pro PSU compatibility

Last month I gave the description of the problem I was having with my Mac Pro on this site and the recommendation I received from Mayer was to replace the PSU. In the region where I live (QC. CANADA), finding a reasonably priced PSU is quite difficult. So I bought another inexpensive Mac Pro with the idea of using the PSU to replace the faulty one. After using this computer for two weeks, I can confirm that it is working without problems so the PSU appears to be in good condition. While performing the replacement, I noticed two differences between the PSUs; the Apple part number and the output amperage (V1, V2, ... V6) which is not the same for all values. It seemed safer to have the advice of a specialist before proceeding with the replacement. Here is the information of the 2 Mac Pro:

The one I already have; Mac Pro 2.1 / 1186 / 2x3.0Ghz / PSU 614-0407

The one bought recently; Mac Pro 3.1 / 1186 / 1x2.8Ghz / PSU 614-0409

Will the 3.1 PSU be compatible with 2.1 despite the differences?

Can 614-0407 only be replaced by one with the same Apple part number?

Another point I would like some advice on is the heat buildup in the compartments where the RAM sticks are located. I compared the 2 machines and after only 10 minutes of operation the 2.1 (8 x 2GB) really gives off a lot more heat than the 3.1 (4 x 1GB). Note that all sticks have the Apple approved heatsink and that they have been dusted. Is it normal that 2.1 produces so much heat in such a short time? Could it be that this heat build-up is a cause of the malfunction of this computer?