I would use the "switching" Boss PSA120S; 100-240 V, 50/60Hz, output DC 9V, 250 mA (not sure here, maybe it is 500mA) (I have 2 units at home and can check latter if you need/want)
polarity is center=negative, outer sleeve=positive (this is the Roland / Boss standard)

Yamaha is just the oposite (outer is negative, center is positive) , take care...
Check YOUR pedal required polarity.

If you need/want to power ALL your effects together (that is, more than 250 mA, or so, you can use a Roland PSB-1U (input 100-240V, output 9V DC, 2000mA, center = -, outer sleeve = +)

Another trick here in some regions of Brazil (Brazil is mainly 127V) where voltage is 220V, is to use an UPS (Uninterruptible power supply ) that is 220 input, 127 output (600Watt). Very popular at northeast of Brazil , that is 220V, but all desktops are the standard 110V...
A bit heavy sugestion, though

regards, from Brazil
Luiz Dias
Watch the videos of me playing the percussion/conga drums with a great band!
--> http://uk.youtube.com/user/footkeys