Of course, that feeding the SIM800L EVB separately with a solid power source is a nice solution.
But playing a bit and knowing the 2 Amp requirement is only required a very short time, I had the idea of simply increase the capacity of C22.
For this experiment, I soldered, as seen in the attached pic, a 1000 uF @ 16 V capacitor in parallel.
The power was always taken from Arduino UNO 5V line.
The module started immediately, working nice, and no auto-restarting.
Removing the capacitor, and the module, fed with the same Arduino UNO 5V line, auto-resets indefinitely.
I have experimented recently with those SIM800 modules with mixed results depending on how they are connected and powered. The most consistent performance has been with an external power supply, actually a type C USB power supply of a reputable make (Raspberry Pi) with the power supplied as directly as possible to the SIM800 with a 470 uF capacitor across the power terminals of the SIM module
I mounted the USB C socket and SIM800 module on perf board like this
Previous attempts to power the SIM800 module from a Nano 5V pin proved unreliable using standard Dupont jumper wires but I made up some short jumpers (5cm) using 22AWG good quality (silicone coated) jumper wires and the module works with those as well
The SIM800 modules are certainly very picky about how they are connected and powered. If I were going to use one in a permanent installation I would, of course, not use jumper wires of any kind and would probably use a reliable external power supply rather than the 5V from the Arduino
