I've just recently bought a new GPU to replace my old one, and am awaiting its delivery. In the meantime, I've decided to have a look at my PSU, since my new GPU has a higher TDP than my old one.

After spending some time calculating how much power my system would drain, I've determined my PSU might have a hard time delivering sufficient power when my computer is at 100% load. Of course, 100% load in this case includes the power surge needed to power on my computer and is a highly unrealistic scenario. Still, I couldn't help but wonder what would happen, if my PSU simply couldn't keep up with my PC's growing hunger for power, for instance when playing demanding games.

Would my CPU and GPU underclock to reduce their power consumption? Would my PC start behaving weirdly, because the transistors wouldn't have enough power to output a 1 when needed? Or would my PC just shut down entirely?


If it's overloaded at bootup, it shouldn't even turn on. If it becomes overloaded with the system turned on, the power supply should detect the problem when it starts and simply shut off, cutting power to the computer to avoid real damage. Not all power supplies do this, though. If it doesn't shut down, the system could crash (with or without BSOD's), things could run seemingly fine for years but have weird, unpredictable hardware failures, or various parts can outright fry.

  • Well, I guess that means I'll have to start looking for a new PSU, just in case. – Nolonar Jun 10 '15 at 21:55
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    Unless your power supply completely ignores the ATX specification or is more than ten years old, it will de-assert its "power good" signal and the computer will harmlessly shut itself off. I haven't seen or heard of PC power supplies that can't safely shut down on overload in about six years. This has been required behavior for more than a decade. – David Schwartz Jun 10 '15 at 21:57
  • @DavidSchwartz. That's good to know. In that case I won't have to buy a new PSU unless I start experiencing issues. – Nolonar Jun 10 '15 at 22:09

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