Maplin > 2.5A Max. Variable Voltage Plug Top Switched Mode Power Supply
That would work, and will almost certainly have the correct connection you need due to the number thats included.
You would also probably get away with slightly cheaper
Maplin > 1.25A Variable Voltage Regulated AC/DC Switched Mode Power Supply
Although that doesn't support 5V, so you would either have to go with 4.5V or 6V. I'd recommend 4.5 if you used this one, as it keeps it within a 10% tolerance of the orignal spec (this is usually what we go on in electronics
)
In all honesty, just go with the top one
(Don't worry about the current - A device will only draw as much current as it needs)