I'm sure you have read this in great detail, are fully aware of the high voltages you will encounter in a flash device and the dangers these bring about.

If you find out that indeed only a capacitor blew up inside, I recommend the following steps:
  1. Make sure some time has passed since you had the flash powered up the last time.
  2. Discharge all electrolytic capacitors and make double sure they are indeed discharged.
  3. Clean up the mess inside as much as you can as soon as possible (caps must be discharged before!!! ). The goo that comes out of electrolytic capacitors is quite corrosive and will readily attack circuit boards and the like. Use whatever it takes to get it out.
  4. Unsolder the defective capacitor. If it was just one of several caps that are in there, try to read the rating from the remaining ones.
  5. Also try to find out reliably, where the plus end of the broken electrolytic capacitor went. If you mistakenly swap polarity with the new cap, it will blow up very quickly.
  6. If there was really just one cap of many that you had to remove, try reassembling your flash device and see whether it works. There is a good chance it will fire, albeit at reduced power. If it still doesn't work, the electric circuitry is likely damaged, and it is up to you to decide whether you can repair it. Don't forget points 1. and 2. before you try this!
  7. Assuming you now have a flash that fires at reduced power, or one that just doesn't have enough capacitors to flash, try to get a new capacitor with the correct rating. Caps with higher voltage rating are fine, but caps with much higher capacity will likely blow your xenon tube. Needless to say you shouldn't get caps with lower voltage rating or much lower capacity. Also try to get new caps and not ones from junk yards, remember you just had the pleasure of seeing what old caps do when they are suddenly charged. New caps will likely be much much smaller in geometry for the same electrical rating, which gives you more options with connecting them correctly - I have never seen replacement caps that would fit straight into the circuit board they were purchased for.
  8. If you reassemble your flash, make sure there is enough distance and/or insulation between parts that carry high voltage. Account for the fact that shock and vibration can and will change these distances.

Good luck!