X and Y are safety classes for capacitors that touch mains. In summary, Class Y is required for capacitors that go mains line to protective earth. Class X (or Class Y, Y can always be substituted for anything lesser) is required for mains line to line.
If you don't have mains involved, you don't need X/Y caps.
(The idea behind this is basically that lightning and giant industrial motors and rogue squirrels and basically all sorts of things are found on the mains. So mains capacitors need to be very strong to withstand that stuff. It's not about the voltages or the currents. It's about the raccoons (the pulsed, very-short-duration, single-event raccoons). No mains, no mains rating needed. But it never hurts, it's just big and expensive.)