Which graphic card is the safest to run on 240w psu?

You really can't add a video card with that low of a power supply. Newegg.com has Rosewill brand that is affordable but still good. If you can afford one at 450w then you can get a video card. The first time I replaced my psu I plugged all the wires in from the new one then took out the old one and installed the new main power box, this way you get it right with no experience. 3bTech.com has power supplies as low as $20, I just don't know how good they are. Sorry I don't have better news for you.