confusion trading out some caps

First of all, I am a novice, so "thank you" in advance for your patience. I'm in the process of changing out some capacitors from the Xover of a budget-speaker. Instead of the common "uF" rating stamped on the cap, a "J" value is given for some. What does this stand for (a competent individual on another forum suggested "JOULE") and how do I formulate the "uF" value from this "J" value? I'd like to choose some replacement caps from the PEx catalog but cannot until I rectify this confusing situation. Thanks!