The 1st one can only withstand 71V max before being destroyed but will hold much more charge than cap b which will withstand 200 volts. The bigger the uF value, the more energy it store.
I agree with 3db on this one. the "uF" is a measurement of the capacitor's storage capacity, as expressed in farads - the electrical unit of measurement for capacitors. The 'u' in 'uF' pertains to the level of capacitance as a negative power of 10 (u =
micro farad, in this case, which is very reasonable for small electronic component circuits). I capacitor with a charge of 1 F (or 1 farad) would contain an extremely high stored charge - you usually see these in large industrial components, or those big, painted caps used for competition car audio systems.
As 3db correctly stated, the voltage rating is the maximum voltage that can pass across that capacitor before it breaks down the dialectric in-between the capacitor's charge plates. Remember, a capacitor opposed a change in
voltage, which makes them suitable for many applications where a regulated power supply would be needed, or a short, mid, long-term RC decay constant (such as slowly dimming lights in your car interior when you close the door, etc, etc.).
If the cap in your sub's amp is rated for 200V, my hunch is that it is in someway attached to your incoming power supply (120V), and is probably used for regulating purposes, to achieve a more constant voltage to the step down transformers. I'm just hazarding a guess though, as I don't have anything to really go on, it's hard to visualize what you've got there.
