Is my psu suitable for gtx 960 4gb.

[DerpyJacob]

My psu which is a xigmatek 400w power supply has a 20+4 power connector.Can this be used instead of the one 6 pin and one 8 pin the gtx 960 requires?

 

[Someone Somewhere]

No. You'll need a new PSU.

The 20+4 pin power connector is for your motherboard, and needs to be connected to that.

You need to use both the 6 and 8 pin connector on the GPU, plus the 4/8 pin CPU power connector.

I'd suggest getting a decent 500W+ PSU - look for tier 1 or 2 on this list: http://www.tomshardware.com/forum/id-2547993/psu-tier-list.html

Xigmatek isn't usually considered good quality in the first place - I'd be surprised if it could output the labelled wattage.