I see many guides using a buck converter in order to power a Rpi using the printer's 24v power supply to step down to 5v. I found this voltage converter but I see that it outputs 5v @ 3 amps. Can a Rpi 3b v1.2 handle that much amperage?
I'm wanting to use the native ribbon-cable camera, which I suspect requires more power than normal (or even if I switched to a USB-based camera). The wall adapter I'm currently using outputs 5v @ 2.1a and I'm getting under voltage warnings on the Pi without any cameras attached.
Current is not pushed, it is pulled, the Pi will only draw what it needs - 3A on the voltage converter is the maximum that it can output. At idle a Pi 3 will almost certainly draw less than 1A. So 3A is fine.
If you are getting undervoltage warnings, then it's normally voltage drop because of the power supply being under-spec'd. I have to say that it's more common with the step down converters than proper wall adapter power supplies. The other thing is that Raspberry Pi normally recommend slightly more than 5V - their power supplies run at 5.1V/2.5A - to avoid issues with voltage drop under load being a problem.