Linear

Linear voltage regulators that throw power away - [1]
Linear reg for 5V, Amazon - [2]https://www.amazon.com/AMS1117-5-0-Step-Down-Voltage-Regulator-Module/dp/B078BCCDN1/ref=cm_cr_arp_d_product_top?ie=UTF8
- Let's say Arduino/RAMPS takes a total of 100 mA at 5V for the Arduino Mega, 100 mA for the Reprap Discount Smart Controller, and 100 mA for everything else. Say 0.3A total draw at 5V - or 1.5W total max. A linear voltage regulator dumps power. If we are using 0.3A, then it is dumping 0.3A * (12V-5V)= 2.1W. Probably works - if there is an advantage for form factor and connectability, we should use this. Existing headers make this favorable. Ideal is a wire on both ends.

Tiny - 5W

Good one, buck regulator - [3]
Solder to fix voltage - 1.5A - [4]
- Disadvantage - needs soldering of 5 small points.
This one looks great - no adjustment needed - [5]
- Has wires already, easiest to connect to Universal Controller
3-pin buck, Adafruit - [6]. Source and specs - [7]
UBEC from Adafruit - [8]