240v psu? lol.. i think all psus are 120-240v....
but umm.. first, make sure its compatible with your motherboard. 20pin powersupply for 20 mobos, and 24pin powersupply for 24 mobos. some powersupplies have 20+4 pins so its compatible with both. you also have to make sure that the powersupply is powerful enough to power all your components or it might give you computer problems.. and even damage your parts.
depending on which parts you have.. they'll have unique power requirements.. if they're high end then they'll need a lot of power. if components are old you won't need such a powerful psu.
components will have power requirements for example 450watts.. but that doesn't mean any 450watt power supply will be sufficient. you also have to look at the amps on the different rails, and most importantly the 12V rail. the more there the better. so what computer parts are you planning on using the psu for? would be easier to tell you what type of psu you'll need. generic psus are the most dangerous because they can dmg your parts. high-quality powersupplies, even if they're weak, they'll still give you problems, but won't damage your parts..
"Is virtue a thing remote? I wish to be virtuous, and lo! Virtue is at hand." -Confucius