to me, this is a bit confusing, so i'll try to make it a bit clearer:
Voltage rating on electrolytic caps needs to be AT LEAST 25% higher than the voltage that's going to be passed across them. However, it doesn't matter HOW MUCH higher the voltage rating is - they'll probably just last a bit longer.
For example, if you need to pass 75V, then you need 100+ volt caps.
>> However, it doesn't matter HOW MUCH higher the voltage rating is - they'll probably just last a bit longer.
Might not be that simple as other parameters are affected as for example ESR which may vary in either direction depending on voltage - sometimes it goes up and soemtimes it goes down. Prices are also a big factor in choosing the overrated (!) value.
(Not to be nitpicky, but not to exceed 75% of rated voltage is not the same as choosing a capacitor with the 25 % higher rating than the voltage needed but choosing one with 33 % higher rating)
My old RT75 power amp from 1975 have Siemens 10000µF/40V and 47 volts across them, since 1977! The amp has been switched on 24/7 since 1988!
If you are a professional you would never do this but as an amateur it can be OK. An easy way to test the max voltage is to apply DC-voltage and then measure the leakage current. When the current exceeds 1-10 mA then you have reach the max voltage. This test takes a few hours because the isolation (leakage) gets better and better if DC is applied.
Suitable equipment is a DVM with 10k or 100k across the terminals of the voltmeter. (= high impedance current meter).