My Recommendation would be to get a 12V only supply and then use a 5V voltage regulator breakout to power the Pixelblaze, just make sure the GND is common to the LEDs and Regulator/PB. This is how I run all my project and never missed a beat. Make power distribution easier. The Regulator sold on the Elecromage shop is pretty good and small, but in reality any one from a reputable supplier will do. In a pinch you can use a 12V Cigarette USB power supply for charging phones etc in a car.
Hope this helps.
I also use a single 12V supply and then a small 5V regulator to suit. There are many such small regulators available. Here is just one example, although I havenât used this one myself⌠Amazon.com: MP1584EN 5pcs Mini 5V Buck Converter Board - 5-30V to 5V, 1.8A Output, Small Size, Black : Electronics
But it also depends on your confidence level with electronics. Iâve been playing with electronics for 50 years at this point, so I tend to do things my way, which is not necessarily the best way for someone with less experience. But regulators such as the one that I linked to are easy to use.
Personally I would stay away from the car socket to USB adaptors - many of them are quite noisy in terms of interference generation. Most importantly, check and double check polarity and output voltage, ideally with a dummy load connected, before hooking the 5V supply to your Pixelblaze. And donât forget that the 0V from the regulator should be connected to the 0V from your main 12V supply.