It'll be best to list your PC spec to see what wattage you require for a start.
This Antec Earthwatts 380w PSU click here, which is ~£38 delivered with cheapest delivery option. It'll do just about most PCs except a high-end one.
May I suggest to never buy those Q-Tec's (or any other bargain basement PSU) again - it's a false economy even for a budget system. G