I know that most computer motherboards use low-ESR caps due to some of the high currents and high frequency ripple, especially in the 3-phase CPU voltage down converter (converts the PS 12v into whatever core voltage the CPU needs at VERY high currents - at least 50A+).
So, a quick search found
LXZ series caps. A couple
35v 270uF version should suffice, especially since they would be effectively in parallel with whatever is currently on there further increasing capacitance adn lowering total ESR. You can do a distributer search
here.
Digikey has them at a very decent price.