why cant i use an external DC power supply to replace the one in the chargers? no reason they cant be USB-c given proper supply but there seems to be some kind of special signaling.
There are vanishingly few AC-DC power supplies that can push 600W (that’s 50 amps at 12V), let alone 1620W (90 amps at 18V) or 3240W (180 amps!!) and definitely none with a USB-C plug on them. You’d realistically be limited to ~1500W on standard household receptacles, and you’d need some hefty cables on the output side of your power supply, especially if you want them to be jobsite-safe. For reference, 180 amps is in the same ballpark as EV fast charging stations; that’s a rough estimate on the size your cord would have to be plugged in to the bottom of the tool.
For the super light duty stuff like an M12 dremel, sure it’s doable. But for any tools that need high burst or sustained power, either a battery or just running the tool on 120V AC directly (or compressed air) is easier, cheaper, and probably safer.
[0] https://docs.google.com/spreadsheets/u/1/d/e/2PACX-1vRghl-44...
For perspective my DC welder is rated at 10000 watts of input. The efficiency is really poor however so I'd only see something like 4000 watts out in the best conditions.