I'm trying to diagnose a faulty car usb power supply. I can't identify one component however. I tried to take a picture
The part on the bottom left. Its light blue and the only thing on it is a big O. I couldn't get a better picture, unfortunately, as it is very small. It sits right between positive power and the resistor above it. I thought it might be a fuse or a diode. Seems not right though, when I use my multimeter in diode mode, it lets current through for a second or two, then stops. Switching the probes shows the same result, letting current flow for a while, then stops. So it might be a capacitor? It shouldn't be, though, as the only other connection from positive input to the rest of the circuit is through another 330uF capacitor, and the input is DC.