Will a 24 pin PSU work in a 20 pin motherboard?

I bought a new PSU without realising it had the newer 24 pin connector and my motherboard is the old 20 pin. I can see plenty of adaptors to allow older style 20 pin PSU's to connect to 24 pin motherboards but not vice versa. Does it matter, would the cable work regardless?

Is the pin layout of the first 20 pins the same? I ask because if I do a bit of shaving between the first 20 and last 4 pins I could probably get it to fit. I even have a crappy old motherboard I could test it with in case it goes a bit Pete Tong.

Alternatively, can anyone point me in the direction of somewhere which sells the adaptor in the UK?

Many thanks!
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wjdashwoodAuthor Commented:
Thanks for the comments. I will study the diagram tonight.
I installed sevral like that, without problems; the plug is keyed for the 20- pin plug also

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wjdashwoodAuthor Commented:
Well to answer this question, I tried just plugging it in and luckily my motherboard had space to accommodate the extra pins which stuck out of one edge. It works fine.

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