The cooling fans on the Creality CR-10 run at 24V, and they're not as quiet as I'd like.
To fix that, I replaced them with Noctua 12V and 5V fans, and I designed a tiny buck converter using off-the-shelf components to output 12V and 5V, along with a custom cable connected to a 5-1/4" PC case fan controller (Thermaltake F6 RGB). So far it works perfectly! (although limited to 500mA)
This design is ridiculously simple, but I wonder if others might be interested in having a simple PCB/module they can quickly connect to their 3D printer as well.
I'm still researching if I want to make this a thing, since there's already many solutions to this problem..
I know I know, buck converters are a dime a dozen, but I really needed something in a pinch so I made this board without researching existing options.
After some research, however, I found that most solutions to this problem involve inefficient linear regulators, some DIY buck converter using resistors (voltage divider), or el cheapo buck converters with questionable parts.