Help choosing a primary cap of a SMPS

[jmibk]

Hi,

i destroyed a main primary cap of a switch mode power supply by drilling through the housing - so i have to replace it.

There are two of them (680uF / 200V), they are in series on 230V setting (there is a switch to switch 230V/115V)
I need the repair quickly, so do I have to replace it with the same capacity? I have one with 1000uF/200V here.

If they need to be the same value, I have two identical 250V/470uF out of another supply. Tue the lower capacity, there will be a power loss on the supply output maybe (that doesn't matter for my application).

Thanks for your answers

[capt bullshot]

They have to be of the same capacity.
In many cases you can use the smaller ones as a temporary workaround, sometimes even permanent, especially if you do not load the supply to its full ratings.

[jmibk]

Okay, thanks for your answer. I got another power supply from a friend.

For my technical understanding:

These two caps are in series and they build up a - lets say - capacitive voltage divider. If they are not the same, the voltage across them isn't the same and thats the problem.
Capacitance of them equals ripple of the primary dc rail. If the ripple is too big (because current draw of any load on the output) the power supply's protection will switch off causing a not stable output at the end.

Are these ideas correct?

[capt bullshot]

Your ideas are correct, I've got some additional information:
When connecting two electrolytic caps in series, you'd also want to use the same brand and type, not only same ratings. This is because of the leakage current should be roughly equal then.
Add the ripple current issue to the second issue: usually a lower capacity one has a lower ripple current rating leading to premature failure (depending on load condition).