Ok so I found this 500w power supply on Amazon which is at the moment £18.50. My question is why is it cheaper than most other PSUs which are £20+ more and have 500w. What's different about it?
PSU: https://www.amazon.co.uk/Silence-Power-Supply-Silent-MOLEX/dp/B00P2GE38C/ref=sr_1_2?s=computers&ie=UTF8&qid=1527591814&sr=1-2&keywords=550w+psu
PSU: https://www.amazon.co.uk/Silence-Power-Supply-Silent-MOLEX/dp/B00P2GE38C/ref=sr_1_2?s=computers&ie=UTF8&qid=1527591814&sr=1-2&keywords=550w+psu