power supplies are one of the important parts in your pc, if your pc was a living thing then it`s the water that it drinks. any 500w or even 400w psu is more than enough for your specs, as long as you buy a good brands such as, corsair, seasonic , cooler master etc, don`t buy chinese brands when it comes to power supplies. here is one that might work for youhttp://www.amazon.com/Corsair-Builder-Series-EPS-80-certified/dp/B0092ML1SC/ref=sr_1_1?ie=UTF8&qid=1406732711&sr=8-1&keywords=corsair+400w
there is even this one http://www.amazon.com/Cooler-Master-GX-II-Non-Stop/dp/B00E9SWH28/ref=sr_1_4?ie=UTF8&qid=1406732869&sr=8-4&keywords=cooler+master+bronze
couger is also a good brand. just make sure you read reviews before you buy anything and the power efficiency on any power supply you buy must be at least 80bronze.