Here's the data sheet if it helps. https://www.cui.com/product/resource/pdqe15-d.pdf
The DC\DC converter is an isolator unit so the left part of the circuit doesn't us a traditional GND, which leads me to be unsure of you -Vo would affect a polarized capacitor. I'm also worried CY2 would discharge into C3 and cause problems.
Also does the rating on C3 matter? the DC/DC converter outputs 24V but the data sheet doesn't mention a specific rating for C3. It does mention ratings for several other capacitors which leads to believe C3 doesn't have to be rated to a specific value.