right, it does seem to be running the code.
maybe the digital pins get disabled with the 9V barrel...
I actually used a separate power supply for the barrel -4,7V and now it works fine...
4.7V? The input to the barrel jack need to be >=7V and <= 12V.
That buckpuck maybe putting a lot of noise on the 9V power line. If you have a 100uF or larger capacitor you could try connecting it between Vin and ground on the Uno
I checked
with a multimeter and it's 4.7v , the blinking on the uno is dimmer but still runs.
You mean like in the image? I'll see if i have around here.
It should NOT work with less than 6.5V on the barrel jack, so something is wrong with your board. The onboard regulator may be damaged.
Do not connect the capacitor as I said.
What to do next is up to you but I would buy a new Uno
I remeasured and it's 4.88V but the fade in/out seems a bit off so maybe it's not optimal at this voltage.
I tested with a new, sealed uno and I have the same issue.
I can live with this set up, just a few more cables.
thanks again for your help and patience!
Should not even work at that voltage, so something is drastically wrong with what you are doing.
Agreed, but i can live with that. 
Thanks again for your precious help!
If it's just a hobby project and no one can get hurt if something goes wrong, then I guess it's OK.
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