I've been running a Uno for years in a dedicated location (garage door open detection). In the last few days it has failed repeatedly. I swapped over the processor board (the Uno) with no effect. Then I tested the power pack which supplies 9 V to the power-in jack. With AC coupling the input looks like this:
Those spikes look a bit of a worry? Or not? That's about 360 mV every 285 µs. Does that look normal? Or not?
The supply itself looks a bit the worse for wear:
Maybe it is a bit tired. What do you think?