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The values are not critical; these capacitors are used for filtering
conducted EMI.

Y class capacitors (hot or neutral to ground) have more stringient
specifications and can be used in place of X (hot to neutral) class
capacitors. Since a short or leakage between hot and ground could
cause a hazardous condition for the user, Y class capacitors must fail
open. X class capacitors just have to fail in a way that they do not
burn and present a fire hazard. You can also use higher class safety
capacitors like X2 and Y2 in place of X1 and Y1.

X class capacitors are available in larger values because Y class
capacitors between hot and ground have to be small enough to limit
ground leakage current. This gets interesting if you have a bunch of
instruments plugged into the same circuit; if their combined ground
leakage currents through their Y class capacitors is high enough, it
can trigger a ground fault interrupter.