I have three DC-DC PSU’s, one for dreamcast, one for playstation, and one for saturn. The only one I use is the dreamcast one at the moment.
It can be especially cool since I live on solar, so my power already is coming from DC from a 12V battery.
The reason it’s not in my PSX is because I have nostalgia for that original gray power cord haha. And the PSU still functions well.
I was also having some signal noise issues like copysave mentioned. in the case of the dreamcast, that seemed to have been fixed when I rewired my dc circuits recently.
The USB power you’re thinking of is USB C Power delivery, and yeah it’s cool. Both PD and the Bitfunx/picoPSU are DC-DC PSU’s. the pico/bitfunx ones are 12v (maybe one of them is 9v) and PD is probably one of those too. You can actually just splice the same cables for any of them.
The most neat use for a DC-DC modded console, imo is that you can now use it with a portable battery bank in conjunction with one of the portable CRTs that also take DC input, making the ultimate consumer portable CRT gaming setup.