In my case, the problem WAS the radio suppression capacitor.
2006 Ford Focus 2.0L
Here are my observations:
1) The radio suppression capacitor, near the passenger shock tower and as described above, has a hot lead that goes from its connector to the "black cube", which is the capacitor itself. This lead is not in a protective loom. The capacitor on my car was dangling, not fastened, it looked like it originally was fastened to a plastic sleeve or mount which had deteriorated, causing the capacitor to now be loose and dangle.
2)The lead passed under a sheet metal mounting bracket, which had a sharp edge. The wire insulation was cut at this point (I'm sure due to general vibration), so the conductor was shorting out against the metal bracket (which was grounded, of course).
3) When the key turned to "run" position, the short circuit described above caused fuse F9, in the engine compartment fuse block, to blow immediately. Upping this fuse (attempt at temporary repair) from 20 amps to even 40 amps did not prevent the fuse blowing. So that capacitor lead really shorts out!
4) I also discovered that a 2nd fuse was blown, a 15-amp in the engine compartment fuse block, I forgot the fuse number, I'm not sure this was part of the same source issue but I bet it was. I replaced this fuse also.
5) Finally, it STILL wouldn't start, and I then discovered the clutch "lockout" switch was bad. Again, unknown if this was part of the same "shorting" issue, or just a coincidence, but did make me go "hmmm".
6) In the end, I replaced the offending noise suppressor capacitor (easy, 5 minutes, $22 seemed to be available at dealer only), the two blown fuses, and the clutch lockout switch.
7) note that the replacement capacitor has a mounting bracket that has a hole in it, for mounting on the bolt on the metal bracket on the car. The oriigiinal capacitor did NOT have the hole, I think it was held on with a crappy plastic jiggy, which then broke and caused this ordeal. So looks to me like Ford revised the part to fix this issue. (As simple as adding a mounting hole is, it's still a revision that tells me "they screwed up" with the original part.)
8) I electrical taped the bejesus out of the new hot wire, since it is loom-less and didn't want to go through this again.
Happy trails.