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I have this strange problem with a new 'XFX' power supply unit,if it is closed from the switch while my pc is running,power supply unit wont start for some time.Otherwise(shutting down pc normally etc...) it works fine.Is this some kind of protection or is it faulty?With an older one this doesn't happen...

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It could be the surge protection.
Nearly all PSUs have internal resettable fuses, that fail when the current exceeds a certain level.
If you switch off the PSU at full load, the violent change of supply voltage induces an immense voltage spike, which can damage the PSU when no flyback diode is built in.

I assume that the fuse kicks in and takes some time to heal afterwards.

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This must be it.It tripped the breaker also 2-3 times but i assume this is because of not enough Amp. – user1478167 Jul 16 '13 at 18:55

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