Mains power, Vic20, is usually AC at 220-240V, or 110-120V at either 50 or 60Hz - to confirm which you use - take a look at the back of your monitor.
It should tell you the mains supply needed, and if not wired through a external transformer, it'll be running directly off the local supply untouched and hence the supply will almost certainly be right.. all you need to work out is which main freq is used.
Plugs - to get you started... you can easily buy in-line plug/socket adaptors to solve a three-pin to two-pin or vice versa (local supermarket here, is selling an international patch kit.. for around 5 UKP, including a decent storage bag for what is about 10 pcs).
Of course, the other way to find out which mains sys is in use, is to touch the mains from the exposed end of a connected-to-mains, unconnected at other-end mains lead.
You'll get a heck of a nasty whack from the test, but depending on your muscular reaction (if you end up with a hand deathlock gripped to the wires.. it's DC and a good current rating upwards of 20A)
Dont try the test, please....., i mention it as a matter of tech note, not as a test to put on the to-do list :P