Jonny GURU's review is for the Hexa HE 400 based on ATX12V v2.3 specs. and only has one (6+2)-pin PCI Express supplementary power connector.
The Hexa+400 is based on ATX12V V2.4 & EPS12V V2.92 specs and has two (6+2)-pin PCI Express supplementary power connectors. Yes it's sufficient to power a system with a GeForce GTX 960.
Overclocking the GeForce GTX 960 takes less than 10 Watts more. The Hexa+400 should have no problem handling that.