Yes, I saw at least a second one on close inspection. My initial diagnosis was wrong though: the Raspberry is connected to the controller board and is working fine. But I realized that the Raspberry should use a 5V power line (when it's powered by USB this is what is available to it) and not the 12V used by the fan and blades.
I looked more closely at the power supply and the cause of death is now quite obvious: through the vents one can see 3 blown capacitors and a dust-like material clinging to the vents and projected on the controller board in front of the vents. By the look of it the material is the same as what is protruding from the blown capacitors. Most likely scenario: these capacitors are part of the 12V transformer and the 5V transformer is independent on this PSU.

The PSU replacement seems the only option...

These are run in ideal conditions : 23°C ambient temperature but I fear the two other miners PSUs might not survive (they seem identical)...