Could you tell us your complete system specs?

At the moment the system is configured as follows:

Asus Z97-A
Pentium G3258
2x case fans
2x CPU fan
16Gb RAM
GTX750Ti
2x HDD
1x M2 SSD
1x SATA SSD

To me it doesn't look like the system would need more than 430w but who knows? And I'm not sure it's a wattage issue since my older rig does the same thing...

Definitely looks like it should be fine, as you say. I have a Seasonic PSU (Seasonic X-660) and it does not exhibit this kind of behavior, you would have noticed it in reviews as well 😉.

Why don't you try googling it and see if you come with something similar for this specific PSU? Could it be a result of some C state that the Haswell CPU supports, but the PSU does not?

Try resetting CMOS by removing CR2032 battery for a while with PSU unplugged from wall, this may help.

Though solidly built the S12-II uses a simple group regulated design that can't cope well with Haswell's C6/C7 states. I'd disable C6/C7 in BIOS.

I have the same issue with my main PC - ASUS P5K motherboard and Corsair RM750 PSU. In my case if you don't unplug the PC from electricity after previous boot, it starts up the usual way, but if you do, the FANs will spin up for a second, stop, then start again with the boot process.

As far as I know, some BIOS settings need power to be set up before boot, that's the thing. The system turns itself on for a few moments before it can boot with said settings.

Anyhow, that's the only logical explanation I've found on the net. I rebuilt my main PC in late 2014 and since then it's been working well despite this starting behaviour.

F2bnp wrote:

(...) Why don't you try googling it and see if you come with something similar for this specific PSU? Could it be a result of some C state that the Haswell CPU supports, but the PSU does not?

TELVM wrote:

(...) Though solidly built the S12-II uses a simple group regulated design that can't cope well with Haswell's C6/C7 states. I'd disable C6/C7 in BIOS.

Thanks. I tried googling this before opening a new thread, but most results seemed to be about people having their PSU start for a few seconds then switching off for good.

I think your suggestions led me on the right track as it appears I might have solved the problem 😀. I couldn't find anything about C6/C7 in the bios but I went ahead and changed the "ErP Ready" setting to "disabled", where it was previously on "Enabled (S4+S5)" - now the computer turns on without a hitch. I am not sure why this setting impacts the PSU so I guess I need to look up what ErP, S4 & S5 are.

RacoonRider wrote:

I have the same issue with my main PC - ASUS P5K motherboard and Corsair RM750 PSU. In my case if you don't unplug the PC from electricity after previous boot, it starts up the usual way, but if you do, the FANs will spin up for a second, stop, then start again with the boot process.

My LGA775 rig has the exact same issue. It's an Asus P5K-E mobo and if I unplug the PSU it will display the same behavior as yours and not start immediately once the PSU is plugged back in the outlet. Now that I know your computer is doing the same thing I guess it's probably not related to the PSU but rather to a setting in the Bios. Maybe something like "restart after power loss"? I'll try and investigate next time I have access to this particular computer...

MMaximus wrote:

... I went ahead and changed the "ErP Ready" setting to "disabled", where it was previously on "Enabled (S4+S5)" - now the computer turns on without a hitch ...

^ Sounds like we might be on the right track. However disabling the whole 'ErP Ready' lot sounds a bit drastic (no more S4 hibernation, and no more S5 soft-off).

I'd try setting again 'ErP ready' as 'Enabled (S4+S5)', or, if you never use hibernation, as 'Enabled (S5)'. Then go to 'Advanced' => 'CPU Configuration' => 'CPU Power Management Configuration' => 'CPU states' => 'CPU C6 Report' and 'CPU C7 Report' and set both to 'Disabled'. This should work, and if it doesn't, you can always disable 'ErP Ready' again.

TELVM wrote:

^ Sounds like we might be on the right track. However disabling the whole 'ErP Ready' lot sounds a bit drastic (no more S4 hibernation, and no more S5 soft-off).

I'd try setting again 'ErP ready' as 'Enabled (S4+S5)', or, if you never use hibernation, as 'Enabled (S5)'. Then go to 'Advanced' => 'CPU Configuration' => 'CPU Power Management Configuration' => 'CPU states' => 'CPU C6 Report' and 'CPU C7 Report' and set both to 'Disabled'. This should work, and if it doesn't, you can always disable 'ErP Ready' again.

Thanks - I couldn't find this exact setting so the closer I could come to was to set "CPU C-States" from "Auto" to "Disabled". I then re-enabled ErP but the PSU went on to do the same on/off thing again so it didn't solve the problem. I have to say I never use hibernation though, so it's no big loss. I vaguely remember disabling hibernation because hiberfil.sys was taking too much space on my boot drive.

So 'ErP ready' needs to be disabled for the PSU to behave.

Group-regulated PSUs, even good ones like the S12-II, can't really cut it anymore with modern hardware. That's why the best brands are moving to DC-DC designs even for the bottom of their lineups (Seasonic will replace the S12-II in the next months).