Your PSU is Tier three.
PSU Tier list:
http://www.tomshardware.co.uk/forum/id-2547993/psu-tier-list.html
Not saying that you have to switch it out. It will do since your GPU TDP is low and it doesn't consume much power.
Lags and freezes are mostly caused by software but can also be hardware related. In your case, i get the feeling it's due to the software.
I can give you basic troubleshooting tips since i'm not a software expert but a hardware expert.
I suggest you do AV (Anti-Virus) scan. After that, update all the drivers. If you use HDD as your system disk, do a disk defragmentation also. Don't forget to check the Task Manager and close or uninstall all unnecessary programs that you don't use.
For monitoring temps, i use Speccy,
link:
https://www.piriform.com/speccy
What OS you use? Win7, Win10 or Linux?