I live in Europe and we have 230V coming out of the power outlet. I have several consumers on one outlet: 5V DC supplies for Router, HDMI-Switch, Ambilight, one Computer, one Macbook and a fan). The Ambilight is just some LEDs controlled by an Arduino. When I turn on the fan the Ambilight flickers for a short moment.
I found this kind of strange and used my oscilloscope to measure the output of my 5V DC power supply when turning on the fan:
The result is quite shocking. I added a 330uF capacitor and the result got better but is still not satisfying (notice that the graphs have different scales one is 5V @ 200ns and the second is 2V @ 500ns):
I also measured another 5V DC power supply and the result was almost the same (amplitude was a little bit lower).
EDIT: After a few MS the output voltage returns to a steady 5V DC.
Is this a problem with my power lines (too many consumer) or just some very bad 5V power supplies?
What could I do to smooth the output of my 5V power supplies (more capacitors? what size?)