Hi,
As so often: A sketch would be so helpful.
***
I can only guess that you are talking about some pri to sec stray current.
If so, it makes a huge difference what kind os power supply you are talking about.
* Is it in a metal case with three inputs (L, N, PE)
* or is it a plasic boxed with only two inputs (L, N)
* or is it some open frame - resued one
* or anything else
Best if you can give a link to the datasheet, atleast give manufacturer name and exact type.
Then We need to knpw how you measured the voltage, which voltmeter did you use?
In any case "heating up controller board and killing it" makes no sense.
If you need help in this you need to provide more informations what this "controller board" is and you need to tell about all it´s connections, wiring, WHAT exactly heated up .. and so on.
Klaus