My computer crashes while gaming, then immediately restarts

[feable]

My computer crashes usually while playing heavy games like Ghost Recon Wildlands. Usually the screen freezes for a second then everything stops. I looked at some other threads and I have stress tested my CPU and GPU but both seemed fine. It also isn't a temperature problem as my temperatures are always fine. Parts:
-Nvidia GTX 960
-8gb ddr3 Ram
-Gigabyte H81M-S2H motherboard
-Compucase HEC-300TC-2WB 300W ATX 2.3 300w
-I5 4460
I think that it is a PSU problem but not sure.
Thanks in advance.

 

[Emerald]

what is the make and model of the PSU?

the Nvidia specs recommend/call for a 400W PSU

 

[feable]

what is the make and model of the PSU?

It is a Compucase HEC-300TC-2WB 300W ATX 2.3
If i needed a new power supply what would you recommend for a power supply.