So which type of Capella are we talking about for FS2?
The real Capella where there are four stars, or the Capella which supports a system of planets?
Are any one of the real Capellan stars far enough away from the others so that stable planetary orbits can form (like in the command briefing animation)? If so, then that star is the one being refered to as "Capella" in FS2, and the one the Shivans destroyed.
If not, then I guess you can assume that Volition took some shortcuts and just considered the Capellan stars as one star "Capella".
But in either case, no matter if the Capella star the Shivans destroyed was a red supergiant or a brown dwarf, one thing is certain: it did go supernova. However the Shivans did it, they managed to make a star -- which might not normaly go supernova -- explode in a supernova.
So whether you figure that that is a regular sized supernova, or maybe a mini supernova, it is still a supernova, and there is still going to be an expanding sphere of intense light (radiant energy: x-rays, ultraviolent, visible light) moving outwards at light speed. And in 35.97 years, people at Aldebaran are either going to see a bright sparke of Capella exploding (like we saw for supernova 1987A), or a gigantic explosion of light which burns their eyes, fries their bodies with radiation, and destroys the ozone layer and boils the oceans of their planets.
Whichever the case, whether just a pretty firework or intense death, now you can know how long it is going to take for the fallout of the Capella supernova (which the Shivans caused however they did) to reach other GTVA systems. So that when you're making your campaign, you can know how many years which systems are going to be affected by however much damage you decide Capella's supernova will cause.