I don't even see the advantages of first converting AC to DC for DC soldering iron.
What's wrong with AC? The only use of DC iron I see is when using it incase mains AC us not available.. And you have a power bank that can supply you with 2 amps, But where would one need it?
Chargers or adapters with output connector in usb shape can provide current well in excess of usb standard any usb2 compliant device cannot offer more then 2.5watts.
It's just exotic item.
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