Provided that your powerbank can provide 12V at 2.5A, then yes, an USB -> DC adapter will work just fine for charging.
…However, why not just pick up an USB-C cable for a quid or two and use that to plug in to your powerbank?
It does seem, however, that power banks that can support [email protected] are exceedingly rare. Mine can do [email protected], but that doesn’t really cut it.
Probably yes if you can find a plug that fits the cube i9 but it is really expensive.
There are a lot of other 12v batteries and you might be able to build one yourself.
12V is pretty common voltage for cars, led lighting and probably a lot of other applications.
Most laptops unfortunately uses 19v. On aliexpress