HPM power-boards, allergic to UV
And all it took was a few years near a window... (the top one is a spare, for comparison)
My experience with recent HPM stuff in general hasn't been good at all, for that matter; nowadays, their name would seem to mean Hopelessly Poorly Made. If their products were dirt-cheap then they would at least have some excuse for it, but no.
Another of the same model HPM power-board is in Mum's bedroom, and has similarly discoloured at its most exposed end. That one wasn't even near a window, either - just an 18W CFL did it. (I'm not a huge fan of CFLs, now, but I have a bunch of them bought in past years.) I intend on replacing it with the spare Arista SPB 1.
If this is how they look just five years after manufacture, can you imagine them lasting 30+ years reliably? Not me.