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I currently have a system with an Intel CPU and an integrated GPU (see below). I am pondering adding a more powerful GPU, say, along the lines of these:

https://www.newegg.com/gigabyte-geforce-gtx-1070-gv-n1070ixoc-8gd/p/N82E16814125893 https://www.newegg.com/gigabyte-geforce-gtx-1060-gv-n1060ixoc-6gd/p/N82E16814125903?&quicklink=true

The specs of my system are as follows:

Motherboard: https://www.newegg.com/p/N82E16813157504?Item=N82E16813157504

Memory (x2): https://www.newegg.com/corsair-8gb-240-pin-ddr3-sdram/p/N82E16820233366?Item=N82E16820233366

Power Supply: https://www.newegg.com/silverstone-sfx-st30sf-300w/p/N82E16817256097?Item=N82E16817256097

CPU + GPU: https://www.newegg.com/intel-core-i7-4th-gen-core-i7-4790k/p/N82E16819117369?Item=N82E16819117369

CPU Cooler: https://www.newegg.com/noctua-nh-u9b-se2/p/N82E16835608016?Item=N82E16835608016

HDD1: https://www.newegg.com/seagate-1tb-st1000lm014/p/N82E16822178340?Item=N82E16822178340

HDD2: https://www.newegg.com/seagate-barracuda-4tb-st4000lm024/p/N82E16822179105?Item=9SIAAY9AWM5481

My question is whether adding the new graphics card will prove too much for the 300W power supply. The estimate I have made was 88W for the CPU, based on the so-called Thermal Design Power or the amount of heat the sink needs to dissipate. I also know that the new card will require about 120-180W of power, depending on the model. This leaves us with about 100 Watts for everything else in the machine.

Basically, the question is whether I should be able to make this work without swapping the power supply. I really like the latter and am not sure whether the company still makes something similar.

How can I estimate the power consumption of the rest of PC?

How much "allowance" and "breathing room" should one have in form of the wattage not taken up by anything to make the system stable and not shut down suddenly because of lack of power?

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    Keep in mind that TDP stands for "thermal design power", not for "maximum power this CPU will ever draw". Intel defines their TDP as the amount of power drawn while running non-AVX code at base clock speeds. Even if you do not overclock the CPU manually, it can still draw a lot more power than the TDP. Both short term and continuous. Long story short: I highly recommend a better PSU when adding a powerful graphics card to this system. PSUs with an SFX form factor exist with up to 700W rating.
    – user13807
    Apr 22, 2020 at 18:03

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We can do the math to calculate the power consumed by CPU cooler, motherboard, RAM, and HDDs for each rail (bus, or voltage specific circuit) of the power supply ('PSU'), relying on the specs of each component. Go back to each manufacturer's website to find their spec sheets; don't rely on the reseller's data, and use the startup current as that's the maximum amperage .

Available power from your 300W PSU per page 4 of the manual: 


Votage * Amperage * Tolerance factor = Max Watts
  Rail  Amp Tlrnc   Watts
  +12V  22  0.96    253W  
  -12V  0.5 0.89    5.3W  
  +5V   20  0.94    94W * Max combined 103W  
  +3.3V 21  0.94    65W * Max combined 103W  
  SB    2.5 0.94    11.7 standby +5VDC

The Tolerance factor allows for variations in the load and line regulation.

For example:

Drive 1, the Seagate ST1000LM014 uses 1 Amp at 5VDC at startup, or 5W on the +5V rail
Drive 2, the Seagate ST4000LM024 uses 1.2 Amps at 5VDC at startup, or 7W on the +5V rail.
But, the Asrock Z97E-ITXac motherboard has no power consumption data, so you'd need to contact Asrock support to find what its maximum power draw would be, separate from the CPU, RAM, and other components.

Adding 120-180W of additional power draw to a system with a 300W power supply is risky, and I would not do it without an accurate verification of what the current power consumption is.

My conclusion: Upgrading the power supply would be wise.

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  • Thanks! I didn't know such wattmeters existed. Sounds excellent :-)
    – MadPhysicist
    Apr 22, 2020 at 16:04
  • Would you recommend a way of telling whether a particular channel (voltage: 12V, 5V, 3V, etc) of the power supply is able to handle the increased load. Am I correct to surmise that only CPU and Graphics Card (6 pin PCI) will pull power from the 224W ~= 12V * 24 A, while the rest will work from other voltages? That is, even if the overall power of the supply seems enough, how can I also confirm that a particular power band will handle the card? Here is the manual I used. silverstonetek.com/downloads/Manual/power/EN-ST30SF-Manual.pdf
    – MadPhysicist
    Apr 22, 2020 at 17:24
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    @K7AAY: your method 2 is an explanation why method 1 is not reliable. Also, some of these power meters can be highly inaccurate for measuring power draw of PCs. I still agree with your conclusion though: I would not trust this power supply with an additional GTX 1060, let alone a 1070.
    – user13807
    Apr 22, 2020 at 17:56
  • Am I correct to surmise that only CPU and Graphics Card (6 pin PCI) will pull power from the 224W ~= 12V * 24 A, while the rest will work from other voltages? Anything with a motor in it, e.g., the CPU cooler, may use the 12V rail. However, unlike most HDDs, the particular models of Seagate drives you specified only use 5V.
    – K7AAY
    Apr 24, 2020 at 15:55

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