We can't tell, because software cannot measure PSU voltages. If you want to measure output voltages, you have to use a digital multi-meter.
By the way, it doesn't matter if you measure voltages "after a few hours of running", or after 5 minutes of running - right now they're both idle. Only the load at the time of measuring counts, however you were loading it before measuring doesn't really matter.
I had a Seasonic G360 that was powering my HTPC fail when it went out of spec with the Power Good signal. It was erratic and sometimes would not come out of sleep because the signal was bad. The PSU was only a couple of months outside the three year warranty so I simply swapped in a new PSU and haven't had any issues since.
So your computer didn't freeze during the GPU test? That's interesting. Maybe you can have a longer test time to make it freeze?
The user on Tom's hardware, I would say that he is so lucky, that he never have been into these kind of troubles. I've seen a lot of strange problems, and everyone will say it is not the PSU, not the cooling, etc. But every time it would end to be the last thing you would expect, not only PSU, but something like a HDMI cable or an old BIOS version.
So when you're facing a problem like random freezes, which you really won't know where the problem is, check these "impossible" components, and it will be fixed.
Seasonic is a good manufacturer, makes good power supplies. I doubt it's the power supply that it's a problem.
However, it wouldn't hurt to test, especially as changing the power supply won't force you to reinstall anything or won't alter your system in any way. As your system seems to have issues even when outside games, you could test even with a cheap power supply (as long as you don't go into games, the 980ti is quite power hungry, consuming up to around 250w when you game)
Such freezes can happen when a device no longer replies to commands from the cpu, for example a video card plugged in the pci-e slot receives a command and cpu gets stuck waiting for a reply... you hear the sound frozen as the sound card repeats the last sound it had in its tiny buffer, because the system no longer fills the buffer with new data.
It could happen due to a faulty usb controller which again may make the cpu get stuck in an endless loop... I've seen it happen once or twice while trying to recover data from some dying mechanical drives (read heads were failing and refusing to move, sata controller would receive bad data from hard drive and freeze and so on)
So it could be anything, like an incompatibility between your video card and motherboard, it could usb related, but I don't deny it could be also power supply related.
People don't generally seem to appreciate the number of issues which faulty or downright broken PSUs can cause. It seems like people who don't know what they are talking about often assume that "PSU supplying current = PSU fine" and "PSU not supplying any current = PSU broken".
I know a smidge more than these people, but still not enough to explain it all.
But yeah, as already mentioned, PSUs can cause systems to freeze. But resets, BSODs etc are more likely to occur when a PSU is playing up.
tldr: with modern power supply from reputable manufacturers and which have certifications and are based on modern designs, typically it either works or doesn't.
No, it's not quite true.
For example, there are components in a power supply that can change their performance (and their technical properties) with heat.
For example, a component may behave as expected in a power supply when it starts up and it's cold, but as the power supply heats up, the technical properties of that component can change slightly (you could say "drift" from normal specifications) and go outside a range that the designer of the power supply accounted for.
A good engineer knows that over time, due to regular use, a particular component may degrade from let's say 100% to 95%, so engineer designs product to work with that component even when that component goes down to 90% of its original specifications/quality.
Well, it could just happen that a component is at 92-95% of this fictional level when cold, but as it heats up its quality level could drop below 90%
Such a bad component could cause the output voltage to fluctuate or have "hiccups" that last for very short duration, like glitches, and such "events" could cause some components to reset or freeze, and then if the computer wasn't programmed to account for these sudden "resets" the whole computer could freeze.
A power supply outputs several voltages: 12v , 5v , 3.3v and 5v stand-by. There's also -12v but that's barely used, it's not worth talking about it.
In some rare cases and with some designs of power supplies, it's possible that if a component suddenly takes a lot of energy from one voltage, the other voltage could be affected. For example, you may have a video card that suddenly consumes 200 watts (for example let's say you're in a game, you pause the game to go in menu, then unpause) and the 5v voltage of this lousy power supply could lower to 4.5v for a very brief time until the power supply can "recover" but that sudden drop from 5v to 4.5v could cause some components to not handle it well.
In other situations, the power supply's electronics can degrade in such a way that instead of 5v, you'll get 5v with a lot of "ripple", basically instead of smooth 5v, you could have a voltage that thousands a time a second, it oscillates between 4.5v and 5.5v or some voltages around 5v.
Chips inside your computer that expect to be powered by 5v are designed with some safety margins and tolerate some amount of fluctuation, but in some rare cases, these chips can just "give up" and get stuck or reset themselves due to bad power quality.
Also... a common failure in cheaper power supplies... the 5v stand-by is a voltage that's produced 24/7 by the power supply, even when your computer is shut down. This voltage is used to power the motherboard's chipset and some components, depending on what you select in bios (for example, the network card could be powered, so that you could turn on your computer remotely if you wish).
Because the power supply is otherwise turned off, the fan doesn't spin, so this tiny 5v stand-by "mini power supply" in your power supply relies on just the air around it to stay cool, so often the components that form this mini power supply degrade much faster than the regular power supply, which is kept cool by fans and big heatsinks.
In time, this 5v stand-by power supply can degrade in such a way that the output voltage starts to fluctuate around 5v so much that it can barely power the motherboard when the computer is turned off.. and as soon as you turn on the computer and the chipset starts to turn on various components in your computer and do its job... naturally it needs more power to do these things compared to when PC is simply turned off. So this brief sudden demand from chipset for more power can be enough for this degraded 5v stand-by power supply to give up or give too low voltage and cause the computer to reset because the chipset resets.
In such cases, you may see computer restarting several times when you try to power on the PC (not to be confused with situations when the computer intentionally restarts itself several times when you install new parts and start for the first time - the bios sometimes "learns" how to work best with components this way, and needs to restart pc a few times for that purpose)
Freezing in general is rare ... more often you will simply see computer shut down or reset itself.
PSU can cause freezing if there is voltage jumps. There are 3 main voltage rails: 12v 5v and 3.3v. If you have low quality PSU, it can go above and below given voltages. Its also known as "Voltage ripple" which can cause instabilities and freeze your system..