Guess that what it comes down to. I will stick with 18650 battery then. It's a lot more small than a big PSU somewhere around my desk ahah
How come every solution you found includes a PSU? A plug in the wall can't give enough power or amps to an ecig and you need to make an electric conversion?
Mains power is AC.
Mod power is DC.
Having attempted and built something similar about 6 years ago; I used a switching power supply that put out 2V-12V and was rated at about 10amps.
The cable is never long enough to take the device with you. Be it to the kitchen to get a drink or to the printer to get a page. If it is long enough, it is awkward and in the way.
If like me, you use your favorite topper most of the day, you would need two "favorites" and another device for use away from the desk.
I made the body from a flashlight tube and mounted a 510 at one end. Without a mosfet, I had to use a huge, expensive vandal proof switch as the tiny momentary switches would fry rather quickly above 2 amps.
My first attempt I used a hole in the end cap for the wires, that device did not stand up (doh) so V2 had the wires inserted in a hole I drilled in the body.
However, since I used an ALU flashlight body, the weight of the wires hanging from the workbench would topple the unit unless I placed it in a holder. (think heavy coffee mug)
I still have the device on a shelf by the work bench, but it no longer gets any use.
IMO: An internal/removable battery device (pass through enabled) and a simple USB cable that can be quickly disconnected and reconnected offers the best of both worlds. I do not suggest you try to reinvent the wheel.
HTH
I