BSOD while playing Dota 2

The cpu test was clean, but the GPU memtest returned a lot of errors on OCCT.
Here's the generated graphs:

Update your System Specifications with Speccy, and then copy this information into your System Specifications: Go to your UserCP, and then select Edit System Spec in the left pane. Copy the information from Speccy into the required fields. These System Specifications will then follow your every post.

It seems you may have a failing or faulty PSU, do you have another PSU to test with or a friend's to borrow for testing?

Unfortunately, I don't have a spare PSU for testing, nor one I can borrow. is there any other way to check if it's the PSU's fault?
(updated my pc info on the cp, thanks)

You could run this additional test for the graphics card, which will rule out the possibility of the graphics card also at fault:

• Video Card - Stress Test with Furmark

I recommend about 1 hour of testing.

Thanks for completing the specs, and how old is your PSU?

Oh, I already run that one a couple times, without any problems (got used to testing graphics cards with furmark since I was sold a faulty one not too long ago).
So can we assume this could be a psu problem? Could you recommend a wattage for my setup? I've been under the suspicion that mine could be a little short (650w)
I bought this psu around spetember of last year, so around 8 months by now

According to the Nvidia website, your graphics card requires at least 450W, I would recommend 850+W, however, I'll ask what others would recommend, here's the specifications for your card:

• GeForce GTX 660 Ti | Specifications | GeForce

Thanks for your advice.
I'll try to save up a little and get a corsair 750w PSU next month.

Well, the graphics card model itself is factory overclocked, here's the reference link:
ASUS - GTX660 TI-DC2OG-2GD5