Weaselboy is right about the failing capacitors killing the power supply in early Time Capsules (except
I think it was just the 1st-gen TCs that had the problem). Note that even though the the PS died, the data was still OK and could be retrieved by removing the SATA hard drive.
Lots of people reported the problem, but it's probably impossible to know the number that didn't have the problem and thus we don't know what percentage were bad.
My 1st-gen TC (bought May 2008) has been spectacularly problem-free in continuous use since purchase. Oddly enough, my serial number falls in the range of TC that Apple identified as being suseptable to the problem. I feel the performance of mine has been very good as far as throughput and excellent as far as wireless stability -- no dropped connections and I've almost never had to power it off/on. It just works. Unless the PS dies!
The first currency converter I came across said 50 pounds was almost US$80. I think that is far too much considering the risk of failure. Even though I love mine and would gladly take another, I'd probably only pay US$10 or US$20 at most...
There is (or was) a list from Apple with "problem" TC serial numbers -- you could find it and check the sn of the one for sale. If it's not on the list you might have a better chance of good luck with it. (But I think it still could fail on you.) Some people have fixed failed PS by replacing the capacitors, some by wiring in an external "brick" power supply. How handy are you?
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On second thought...
I didn't think about the value of the 1 TB hard drive. It should be fine. So, if it were me, I'd pay about $15 above what I figured the hard drive was worth to me.
