Hi I would also NOT putting caps in series in A SMPS . these caps work with High ripple .
putting a slightly high uf @ same voltage maybe ok depending if the mosfets that come after it are up to it.
May put excess strain on the rest of the circuit .
As someone else also mentioned . Should only use High ripple caps (surge) without getting too technical .
KM are Surge rated .
If you do try. keep your face clear these 400v caps can turn nasty
specially if you use second hand .
First Remember the first Law of Murphy What can happen Will Happen .
All Safety measures should be used .. ( get some one else to turn it on )