A few months ago, I built myself a new server and from the outset it had that smell of new electronics breaking in. But the smell never went away. Not a burning smell, more like electrolytic caps. I'm always alert for scorching odour.
Today I needed to open up the system and unplugged its power cord and was surprised to find green slime on the contacts. Admittedly I mated a new power supply with a cord that is probably 10-15 years old.
It has a slight dimple on one face which makes the lettering appear curved in the photo.
Any idea what caused this?
The green-ness is a dead giveaway that this is one or more copper compounds, from corrosion of the contacts inside and/or the metal of the pins in the IEC socket.
Many copper compounds are green. The "verdigris" that makes the Statue of Liberty green, for instance, is primarily copper (II) carbonate. In the case of your goopy power plug, the wetness of the goop means that if the computer isn't sitting under a roof leak, there must be a hygroscopic (water-attracting) compound in there. That rules out copper carbonate, but there are several other copper compounds that'll suck water out of the air to one degree or another.
I think this process can be self-accelerating - a tiny bit of the hygroscopic compound is formed, it sucks up some water which dampens the area and accelerates the corrosion, and in the case of an electrical contact may further accelerate the reaction by increasing resistance so the area warms up. It's the warm copper compounds and/or plastic that's making the funny smell. It's also possible that outgassing from the plastic of the plug on the back of the new computer, or degeneration of the plastic in the old cord, has contributed to the reaction. Cable insulation is normally made from PVC, which stands for polyvinyl chloride, and every link in the PVC chain has a chlorine atom just waiting to be liberated, so I wouldn't be at all surprised if there was copper(II) chloride in the slime.
You can see similar green compounds discolouring the edges of copper or copper-alloy fittings in clothing, like riveted jeans or brass belt buckles. The copper compounds form a sticky goop there that's probably based on clothing fibres, sweat and shed skin flakes, all coloured (and flavoured!) by the copper compounds. (I presume hipsters who never wash their jeans develop particularly impressive rings of green goop.)
Fortunately, none of this is a big problem. Just discard the old IEC lead, make sure the pins inside the plug are clean (a pen eraser should be adequate to remove any tarnish), and plug in a new lead.