12V/240V -> 12-20V laptop power supply with 12kHz whine

[moz]

I bought a cheap UNIVERSAL100W 12V-24V 5A Max Laptop AC Adapter Power Supply Charger with Carplug  off eBay for $40 (did not come with car plug, but I didn't want that anyway). It actually works quite well for my intended purpose - running the laptop off a 100AH 12V SLA in my shed. Laptop draws about 20W so it's no big strain on anything, but it runs noticeably warm to the touch. Opening it up there are a few tear-down comments:

• some of the end-cap screws are pre-stripped for your convenience
• only the display driver chip has had the markings ground off, and that was done badly
• there are isolation slots in somewhat random locations, and plastic-coated isolation barriers under the main board and between the 240V input and rest
• the transformer seems really awful to me
• there's a weird tiny contact between the inside heatsink and the case

The really annoying thing is that there's a 12.1kHz whine coming out of it, and I'm not entirely sure exactly where from. My inclination is to hot-snot or silicon the inductor and see if that helps, but I'd appreciate the expert opinions of anyone with an oar to poke in. Am I likely to wreck it by running amok with some silicone sealant/glue (construction adhesive), or with a hot glue gun (assuming I steer clear of the heatsinks)?

I will take better photos tomorrow with a proper setup, but for now here's some cellphone snaps to hopefully give you some ideas.

[capt bullshot]

Don't use random silicone for electronics. Some of them realease acetic acid.

[moz]

Metal case without double insulation nor ground pin, fail.  For 99.9% of time it won't kill you, but I bet you don't want to take the chance. This is a proper AC/DC input laptop PSU, and it is very affordable.

Sadly "This item does not ship to Australia.". But I can buy it here... for $90.

I do take your point about the lack of grounding, but I have no intention of plugging it into 240V ever, for that reason. I bought the supply because there's no mains in my shed, which helps me avoid that temptation. The mains cable supplied is also a cheap non-approved chinesium one that was surprisingly rigid for its diameter.

[amyk]

You can use a drinking straw as a stethoscope to determine which of the magnetics is emitting the whine. It might be a ceramic cap too.

[moz]

The noise is worse, and I have a better spectrum, again using a simple spectrum analyser on my phone. But I'm also having (more important) issues with a new solar charge controller only giving about half the expected output, so I have not opened this thing up again yet.