I am using a few of the LED Driver boards with Xiao C3s. I have only completed a 5v run with this setup, but I am finalizing mounts for a separate 12v run.
Initially on the 5v run I had a Y-connector going to 2 loops of 60x WS2812b (5V). I limited the current in WLED to 2.8A at 5V and had it powered through a 5V/3A USB-C PD hub (Anker). I measured the 5V-out pin at the base of the LEDs and saw less than 4V at low brightness.
I tested and saw option A in my pic outputs the same voltage as the barrel input. I am now injecting power from there to the end of my 5V run, and am seeing very close to 5V out on the other side when the LEDs are on and connected. I read that I can power 5v lights with a 12v PSU but I’m not looking to do that here.
Is (A) an appropriate (or the best) spot to pull power from on this board, assuming my barrel voltage matches my LED strip voltage? Does the answer change if I’m using a 12V barrel with 12V LEDs?
So , I would refer you to the schematic and wiki for further clarifications, However it is a powerful little board, The A item you call out ARE inputs (only) albeit an in Parallel connector selection is really all it is, However unadvisable to use one as Tee or 'Y" of the 12v Power supply, bad things can Happen if done like that.
The design idea was to keep a consistent set , Barrels for 5V and 12V Wall-worts or power bricks. and terminal Blocks for discrete supply connections, bare leads etc.
Don’t mix and match if you can help it. something is bound to cook Use a good 12v power supply and 12v strips , It’s bad A$$ with the Xiao controlling the status by WIFI or BLE
Understood about not using those terminals. I don’t totally understand power injection and am not sure how much current actually gets passed in that ‘loopback’ scenario.
Assuming 5V source, 5V LEDs, is the right solution for voltage drop to split the initial output from 5V/A0/GND into 5 (2 +, 2 -, 1 data), where 3 go to the 120 LEDs, and 2 connect at the end of those same LEDs? Hopefully my diagram helps if unclear.
Use a good 12v power supply and 12v strips , It’s bad A$$ with the Xiao controlling the status by WIFI or BLE 
PJ 
