ITX PSU (12V Brick + DC-DC PCB) weird GND/earth connection

[neo2001]

Over a longer period of time, I got some power supplies, from different sources, that are supposed to be used with small (Mini-ITX) cases. The external part is a power brick with a DC output of 12 V (some use 19 V or more). Inside the case is a small PCB, which creates the other voltages needed (5 V, 3.3V,...). These come either already installed with the case or can be bought separately.

Both parts are connected using a regular barrel jack (5.5/2.5) on the backside of the case, which is connected internally to the mentioned PCB. The PCB itself provides the ATX connector(s) usually needed.

The barrel connector has 3 contacts: tip, sleeve and insertion detection. Insertion detection is connected to sleeve as long as no plug is disconnected. If a plug gets connected, the insertion detection pin is mechanically disconnected from the sleeve.

Now the weird thing is, that all these PSU combos use a green/yellow wire that is connected to this insertion detection pin and are supposed to (or simply are) connected to the metal case. But I don't understand why? I would understand, if this wire would be permanently connected to the sleeve, for a better GND/earth connection to the case, but this way it actually gets disconnected when the plug is inserted. In the end, it doesn't matter, since DC GND is connected to PE/Earth anyway through the power brick and the standoffs of the PCB. But there are multiple devices that do this, so I don't think it's a mistake of a single device.

What could be the reason for this connection?

[agehall]

You can’t really have PE in a standard barrel jack since it only has two connections (+ and GND). Makes me wonder if this is some sort of contraption to counter ESD when the computer isn’t plugged in..?

[ArdWar]

This is PicoPSU (clone?) kind of thing right? Why do you assume they know what they're doing?

[neo2001]

Yes, some power "bricks" (if they even have earth connection) seem to connect GND to PE/Earth either directly or with a certain resistance in between.

I think connecting the case to the detection pin is either some kind of genius move I don't understand or simply makes no sense, and they just copied this from each other without understanding why.

[neo2001]

This is PicoPSU (clone?) kind of thing right? Why do you assume they know what they're doing?

Some of them are sold by reputable brands, like Chieftec:
https://www.chieftec.eu/products-detail/192/Adapter___DC_to_DC_SERIES
https://www.inter-tech.de/productdetails-155/ITX-601_EN.html

But there are also cheaper ones on AliExpress and eBay with a "simplified" layout. But they probably can get away with this, because it's only a DC to DC conversion and the system powered by those usually only need 15-20 W tops anyway. For the AC part, I tend to use a known (laptop)brand.

[JustMeHere]

Since you don't need to switch from battery power (and detect it) there is an extra wire.  It's a good idea to ground your case.  So why not save some money and use the spare wire?  There might even be a bit of EMI benefit by keeping this connection away from the PCB.