I've been through a true power failiure where you have nothing. That is by any standard NO FUN! If anyone says that safety was not comprimised they are telling a rather large lie... Unless of course there is no traffic... If you are using radar separation and then have no radar you have to go to non radar and you have a lot of what we call here in the states, "deals". Now, like I said, if you don't have much traffic, then not much of a problem, but if you are working departures, arrivals and a lot of crossing traffic, that is a bit different... Can't see or talk for ten minutes, that is no fun...
regards