Mains power issues

I live in the UK and currently move my PC between 2 houses, one in London and one in Oxford.

When I am in London my graphics card is subject to random crashes, but when I am in Oxford the PC has absolutely no problems whatsoever. The only thing that is different in the two setups is the house the computer is plugged into, making me believe it might be something to do with the mains power.

Someone recommended that I get a UPS so that the power going to the PC would be cleaned up but having had a look, UPSs seem to be very expensive. Seeing as I don't need a UPS to actually run the system in the event of a power cut (they almost never happen) is there a cheaper alternative?

I'm running a single Asus GTX 560 Ti, my PSU is an old corsair HX620 that has never had any problems before.

Sounds like you need a line conditioner?

http://www.tripplite.com/en/products/product-series.cfm?txtSeriesID=838

Line conditioners all seem to be made to provide multiple outlets (i.e. for server rooms I guess) so the ones I found seem to be more expensive than personal UPSs.

Cheapest I could find:

http://www.amazon.com/Tripp-Lite-LR...?s=electronics&ie=UTF8&qid=1363198772&sr=1-85

Shouldn't the power supply be cleaning up everything? It's not like the mains voltage is going straight to anything in the system. I'd think any decent PSU should clean up the power well enough to never need anything more.

The only power issue I could see happening like this would be if the mains power was sagging, which a don't know that a line conditioner would fix (at least not a sag enough to make the computer crash).

Have you tried other places in the "problem house"? That could rule out a bad outlet, etc.

(and I'm not an electrician, so I could be completely wrong on all that I said)

Funnily enough, it has only happened once in the past week of using it in the problem house (same wall outlet as before). So perhaps the issue with the mains was only exacerbated in December for whatever reason. The interesting thing is that it's just the graphics card that seems to crash, not the entire system.

Perhaps the mains sagging is enough to lower to the power the PSU can output to the system only enough to affect the, proportionately to the rest of the system, power hungry PSU but not the rest of the components?