PC Randomly rebooting, no BSOD

[Alastuor]

Hello everyone, I've been having some problems with my pc lately, in the form of random reboots without any kind of warning.

It started almost a month ago and most of the times it happened while gaming, although I've had it happen a couple of times while browsing and once while idling; I had a week without any problem, then it started again without me having changed anything in the system.

I've successfully run prime95, furmark and memtest86, CPU temperatures were always below 55°C, graphics card's around 65-70, I even set a new record of total power draw (compared to gaming) without crashing.
Event viewer only shows a generic kernel power ID 41 error, I deactivated "automatic rebooting" to try and get a bsod with some info but it still reboots despite that.
A BIOS reset did nothing.

This morning I got 2 reboots while playing, one while browsing the internet 3 minutes after the last time it had happened, and one while sitting on the BIOS, which excludes every possible OS-related issue (doesn't it?).

Now, I have a strong suspicion that my PSU might be the culprit but I don't have a second one to spare and I'd like to avoid getting a new one only to discover the problem is still there.
Is there anything I can do to narrow it down even further? Are there tests that a technician could do to determine if it's actually failing?

Hope I haven't forgotten anything, many thanks to whoever answers

My system specs:

Spoiler

• 
  ■P8Z68-V pro
  ■i7 2600k (never overclocked) with corsair H60 heatsink
  ■4x2gb DDR3 vengeance 1600
  ■Gtx 770
  ■Samsung 840pro, wd caviar blue, seagate barracuda
  ■Nexus rx6300 psu
  ■Windows7 sp1

 

[neon neophyte]

its probably the psu

 

[alexoiu]

I agree. You should firstly rule out a power supply issue. Try RMA-ing it, if under warranty.

 

[Alastuor]

I agree. You should firstly rule out a power supply issue. Try RMA-ing it, if under warranty.

It's not under warranty anymore (almost 4 years old) so that's not an option. Unfortunately I'm not properly equipped (nor even remotely experienced enough) to test the psu myself, so I was thinking of contacting someone to do that for me.

The thing is, this problem has been random from the start, some days I wouldn't notice anything, some other days it would reboot several times, and I've had a whole week with no problems at all, so is it possible for a professional to detect this kind of fault without having to wait for whatever it is that triggers it?