Hi,
Its the thing with the capacitor only getting change current for a small time due to the poor power factor operation.
Ill append the LTspice if you wish. (its attached now)
Its 269mA AC RMS ripple at 220vac in and 15w out.
Attached is the ripple current scope, and the FFT of it....it shows the majority is at 50-800Hz (unless the Blackman-Harris FFT function got it wrong)
Can you post the assumed schematic? Also, are you using the recommended circuit design for your PSU, including the NTC and EMI chokes?
I think there is actually a fair amount of energy at higher frequencies, although I'm glad to see it is down -320dB @ 100MHz.
Try replacing the PSU circuitry with a resistor that draws exactly 15 watts and see what the calculated RMS is then. I'm thinking that the various parasitics in the circuit will blunt the peaks enough that your ripple to load ratio will be less than an incomplete LTSpice simulation shows. I would at least try to experimentally measure it in an actual circuit before you go into production. Just based on experience and observation, 33uF is not a small primary filter cap for a 15W PSU, and even lower quality third-tier caps are usually not the failure point in these types of supplies.
In any case, I think your (or my) selected capacitor will likely outlast this economy PSU module. If you really want to worry about something, start looking at the secondary capacitors.