Guys, wake up to server PSU's! they go for a pittance and are more robust than an equivalently rated (wattage wise) boxed PSU. Fifty bucks may sound like a steal until you find out an equivalent 2nd hand server PSU is 15 bucks give or take.
A server PSU's that would adequately power an overclocked S3 (and then some), can take the shape of:

http://store.vibrant.com/Dell-HY104.html?utm_source=amazon&utm_medium=ads&utm_campaign=Dell-HY104

also at fleabay

http://www.ebay.co.uk/itm/Dell-PowerEdge-1950-Power-Supply-HY104-0HY104-Z670P-00-7001080-Y100-PSU-/360931800592?pt=UK_Computing_PowerSupplies_EH&hash=item5409363610