Just fixed a Linksys BEFSR41 v2. Seems that the power brick had a standard cylinder DC plug however the central bore was about 1mm larger than the socket's central pin. I originally thought that I just had a 3rd party powerbrick, however a colleague of mine recognised the router and explained that it was a similar problem for him. Maybe a dodgy batch? Anyway the DC socket was a standard part, the warranty was void through age anyway so a cheap replacement, £1.11, has fixed the problem.
Better than new.