Looking inside PSU for clues if it would work on different voltage
is not something I would recommend for most people because
it can be dangerous. Why not read the print on the side of the
PSU? It must clearly state operating range (90-150VAC 60Hz or
85-250VAC 50/60Hz). The first case obviously wouldn't work
while the later one would. Trying to determine operating range
by loking at capacitor alone is not good practice because often
they are overrated or it is not just one cap that does the job
(it's often two in series so together they can work with higher voltage).
For example this is used in PC power suplies so that input voltage can
be easily selected via simple slide switch.
Nigel is right. The safest way to run US PSU in Europe is to use transformer to lower the voltage. There are also small power
converters for travelers. They probably cost as much as your
printer ($50-70) so make sure to check for power requirements
next time you buy a product in different country.
Another thing to consider is approvals. I'm not sure if you would
have easy time explaining to insurance agents that your house
didn't burn down because of equipment lacking CE certificate
or your tinkering inside PSU.