Hi Folks -
Was shopping on Parts Express for some caps. Saw some 10000uF but from the pix, not obvious how to tell poles. Submitted a question that got the following answer. Thought it might be helpful to post. Apparently not all caps are "polarized". From the little reading I did, a cap intended for use in an AC circuit can't be. At any rate hope the below is helpful. (it does confirm some of the info previously posted in this thread)
From Russ at Parts Express -
"If a capacitor is, indeed, polarized, then there are a few different indicators you can look for. If one lead is longer than the other, the longer lead will be positive, the shorter will be negative. You can also look at the end caps, the positive end cap will generally be black plastic, rubber, or some other insular material, while the negative will typically be aluminum. Many are also marked clearly, with plus and minus, or an arrow pointing from positive to negative, or a stripe on the negative side. The capacitor in question here is an electrolytic capacitor, non-polarized."