Conclusion: best choice 600/650 watts
In the segment above 600 watts the Corsair AX650 is our favorite. This PSU is also semi-passive and didn't make a sound in our noise test. It's almost 90 percent efficient, has ripple values below 50 mVtt, has longer cables and is modular - a top model in every aspect. It's no secret that this power supply is based on the Seasonic X-Series 650W. On their product pages you should compare their interior photos, it's really obvious. The Seasonic version scores a hair less and is a little more expensive. A good second place!
The Corsair AX650 costs an average of £105. If you want to spend a lot less and still get a good quality PSU, then the Nexus NX-6000 R3 is a great option. It's extremely silent, has 86 percent efficiency, and only the ripple could have been a little better. The Antec High Current Gamer HCG-620 is a good option for overclockers, a little less silent, a little less efficient, a little more expensive, but a much lower ripple.
Among affordable modular power supplies the Chieftex SPS-650 is the best choice, but you're making a compromise. Every aspect is good, but nothing stands out.
Corsair Professional AX650 650W
Nexus NX-6000 R3 600W
Antec HCG-620 High Current Gamer 620W
Conclusion: best choice 700W
The number of 700W power supplies we received was a bit disappointing. That doesn't stop us from recommending the Be Quiet Straight Power E9 700W. It's extremely silent, efficient and its ripple is more than low enough. It's not modular, but its price is decent for what you get.
Be Quiet Straight Power E9 700W