Nope, they aren't compatible.
A 7850 requires dual 6pin connectors, while that PSU only has one.
The 550W version of that PSU will work though.http://www.newegg.com/Product/Product.aspx?Item=N82E16817207013&Tpk=xfx%20550W
thanks for the reply, how do i know how many connectors i've got, i have found for UK not from newegg as they don't deliver to the UK. If you could explain would be great thanks again http://www.novatech.co.uk/products/components/powersupplies/p1-550s-xxb9.html
if it is this - PCI-Express Connector - 1 x 6-Pin, 1 x 6+2-Pin
i am pretty sure the other psu has that aswell
Edit again: i have realised the others are 1 x 8-pin along with 1 x 6+2
could you please find me the version you found but for UK? thanks again