Do you have pictures of the defective area?
This is a view of the capacitors, you can't see them whole through the vents but you can see they are all opened instead of having a flat metal surface. The one on the top left shows the material best.
This is the material still clinging on the vents.
This is the projection of the material mostly on the edge of the controller board in front of the vents:
And finally the verdict is: both blades died with the PSU.
I found a replacement PSU that I had in storage (a brand new high quality 12V 300W PSU for large LED lighting setups) to test the a2mini and here are the results...
What I believed to be a 5V line is in fact 12V (the red wire used for it is a mistake). The wiring color is wrong for the high voltage wires too: ground and neutral wire colors are swapped. You can't replace the PSU with a standard ATX one: the connectors aren't wired like standard PCI-e: the 12V and ground connections are swapped. On one of the blades there was an extra PCI-e connector whose wiring might have been standard but it was too close to the fan to be used (and the other blade doesn't have this connector).
This a2mini had other problems: I noticed a bent capacitor and one thermal pad not properly aligned on one of the blades and corrosion around the screw holes on the side panel holding the PSU. I really hope the 2 surviving a2mini will not blow up like this one.
I just asked for a refund or replacement.