Powering 5V Accesories I'm using an Uno to control NeoPixels LED strips (60 per metre). These are powered with a 5V DC supply. Now, when using USB to power the Arduino it works lovely. However I want to move the Arduino into a standalone "installation" where I'll only want one power supply. 

I've already got a 5V DC supply which outputs about 5.2V. What is the best way to power both the Arduino and the LEDs? I understand the need for at least 7V at the Arduino's voltage regulator input. Would my best bet be to get a 12V supply (or similar) and use a buck converter to power the LEDs? The total current draw could reach 3.6A but will be 400mA for the majority of the time.
If your supply is regulated (put a 47ohm resistor across it and measure the AC voltage with a DMM; it should be almost nothing if properly regulated) then you can use it for both the Uno and the NeoPixels. The ATmega328P has a maximum input voltage of 5.5V, and the WS2812B has a maximum voltage of 5.3V, putting the supply within the proper range to run them.