How to connect an Arduino to a Pc and an external psu?

I am new to the world of Arduinos and have a question about powering my Arduino Nano. I am using it to control LED’s (around 400 WS2812b LED’s) with the Neopixel library and managed to write a script for controlling multiple LED strips at one time with different effects. I have also added a serial communication with a python script but now I don’t now how to power my Arduino the right way. I want the Arduino to have a connection to my PC for the Python scrip and I want the LED’s to glow pretty bright so I bought a 300A 5V power supply for them. So when I run my PC, I can control all my LED’s like I want, but I also want to control the LED’s without running the PC. So do you have an Idea how to do this (I can’t connect the Arduino to the external psu directly because of the PC connection right?)?
Thank you for your suggestions :slight_smile:

Minus side of 300A 5V supply connects to Ground (GND) of Arduino and Ground of LED Strips. Plus 5V side of 300A 5V supply goes to +5V side of LED strips. That way the Nano is powered by USB and the LEDs are powered by the 300A supply.

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The power supply is 5V? Connect its Gnd to the Nano Gnd, and it’s 5V supply to the Nano 5V line, and the LED strips in parallel.
There is a diode that prevents the 5V line from backdriving into the USB port, see attached. Do not connect 5V to Vin.

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Ok, thank you for your solution!