installing caps backwards

[Reece]

Wild stuff! Technicolor: re: confusing markings on modern electrolytics. Look at the ends where the wires go in. The negative wire connects to the outer aluminum can and the can end is exposed at the negative end. The positive end has a fiber insulator and you don't see the can.

[N2IXK]

And on radial lead caps, the longer lead is generally positive.