Before I begin I just want to apologize for my mediocre understanding of things electrical and arduino. I know there are a lot of topics similar to this but I'm confused by the term external PSU
Do I need to worry about any sort of issues (loops/grounding) if I use the molex connector to supply power to my arduino uno and continue to use the USB for serial communication at the same time? The source of both would be from the same PSU in my PC.
From what I understand the Uno when powered by DC should not exceed 7.5V for maximum efficiency. So it looks like the 5V from the molex would be more suitable than the 12V and sufficient for my needs of roughly 3.6A (60mA per LED * 60). Since USB can only supply a maximum of 2.0A and Molex appears to supply up to 5.0A from what I've read.
And I would connect it like so 5V molex powered Uno?
Currently I'm using the arduino uno to power a single 5V strip of 30 rgb WS2812B leds, which works great when powered through the USB port, but since I need an additional strip of 30 leds and USB alone cannot supply enough amperage to power both I need a better source of current. I also needed the cleanest solution possible as it's for a PC tower and I don't want to use an external power source.
Edit - Alternative solution
If you have an Arduino board with USB, simply power the Arduino from your PC's USB via a standard cable and the LED strips from the Molex. The only connection between these two would need to be GND and led strip data line. No need to share a 5V between the LEDs and the Arduino