What country are you in? It helps to know.
I've got the same pedal. The power supply that came with it was a 12VDC 1A output. That's right, DC output! It worked no problem. What I'm not sure of, if the polarity at the tip was standard Boss style. I think it was. I can check but it might take me a while to dig it out. I have things buried in boxes.
Whichever way, I went and bought another power supply (AC output) because I wasn't sure if the DC would cause problems. I eventually did find out if DC output would cause problems and apparently it won't if the polarity is correct! Go figure. I could've saved myself some $$. It's also easier to find 12VDC power supplies!
I bought a typical 'laptop' style power supply, regulated, *similar* to this http://www.radioparts.com.au/product/33771335/sm1240-12vdc-4a-switchmode-power-meps-class-iv-2.5mm-cen-tve#.U99ho01-8uU (NOTE: the one shown is DC output, mine is AC output) and have had no issues with this style of supply. I bought it ages ago and can't find the place I bought it from (I live in Melbourne, Australia)
Here's another from a store in Melbourne, Australia http://www.radioparts.com.au/product/33770080/ac1210-12vac-1.0a-ac-power-supply#.U99k_U1-8uU
One thing to remember, the supply should be a minimum of 1Amp output. It doesn't matter if you find one 2A, 3A or 4A. Just make sure the output voltage is correct (12VAC).
You should look for a power supply that can take an input voltage between 110V-240V, that way you don't have to worry about this again. Most laptop type power supplies are multi-input voltage.
Type in buy 12VAC 1 amp power supply in google and see how you go. Depending which country you're in type in buy 12VAC 1 amp power supply in <insert country>
If you're in China (China is 220V); China shares the Australian socket connector shape, just upside down..... http://shoppingshopping.com.au/Miscellaneous/Unbranded-North-America-US-3-pin-to-Australia-Power-Adapter-Plug-PA-3515-p1p-20983-146.aspx) and another http://www.travelchinaguide.com/essential/electricity.htm
You don't need to change anything on the pedal. Use proper power supply, plug in, switch on and play.
Hope this helps.