Dont bother with the step down coverter. All PS3 's have universal psu's. Just go and buy a power cable for a pc and put a 3 amp fuse in it. Ive been using mine like this since it arrived at the begining of December and no problems.
If you dont belive me have a look on ebay and people are selling them for about £8 you can buy them for about £3 or you might have one hanging about at home.