I'm searching for an ATX power supply which is powered by a 12V input. Peak power 300W.


  • 1 standard ATX mainboard connector
  • 1 4-pin cpu power connector
  • 1 6-pin PCI-E power connector
  • 2 SATA power connectors (5V is enough)

Input: 12V.

I found various power supplies which provide only the first two connectors. Now I can improvise the SATA connectors (step-down the 12V to 5V, wire up the connectors, done), but the PCI-E connector isn't that simple I think (has a sense line to compensate for voltage drops).

A sufficient answer would either be the power supply I described, or if someone knew if it's possible to drop the sense line from the PCI-E connector (and if the answer is yes), then that would also solve my problem.

  • Can you spell E-X-P-E-N-S-I-V-E ? Buying an inverter and suffering the energy lost will get you ahead for a very long time.
    – SDsolar
    Jul 6, 2017 at 5:30
  • Actually the reason it's 12V is usually that this runs from a battery and batteries tend to have some limit on the energy they store... so no, it doesn't make sense to just "suffer the energy lost" (and the added couple kgs of weight). Plus those PSUs aren't that expensive, and I sure as hell won't need two.
    – Nobody
    Jul 6, 2017 at 20:27

1 Answer 1


Caution: 12@ 300w is 25A. You need 4 gauge wire to handle that kind of load. All the ones that are 300w or more require 16v-20v.

You would need to combine 2 to get a full 300w all the time.

You will probably need 2 of these devices to provide the correct number of amps to the PCI-E device. Also 1 might overheat under load

You will need a molex Y cable simple to connect to the add2psu unit so PSU 1 turns PSU-2 on automatically.

Here is 1 option: (250w) peak (300w) http://www.mini-box.com/M4-ATX?sc=8&category=981 When operating at constant 160 watts or more forced ventilation might be required.

PSU chart 250w option This picture seems to show 2 sata and 1 molex.

molex to 6pin https://www.newegg.com/Product/Product.aspx?Item=N82E16812423173&ignorebbr=1&nm_mc=KNC-GoogleAdwords-PC&cm_mmc=KNC-GoogleAdwords-PC--pla--Cables+-+Internal+Power+Cables-_-N82E16812423173&gclid=CjwKEAjw1PPJBRDq9dGHivbXmhcSJAATZd_B-pm9o4gStz3wqfXlWnmmOzv0yjspZ5CSOi-aS7ptEBoChGbw_wcB&gclsrc=aw.ds

http://www.add2psu.com/ Turn 2nd PSU on

Also some Y adapters.


  • So you (or this adapter cable you linked?) are saying I can just drop the sense line which the PCI-E spec asks for (as in "require"). Could you please confirm that you know that this is okay? I wouldn't bet expensive hardware on some random adapter-producer following best practices. Also, I really meant the "peak" in "Peak power 300W", so I won't need two PSUs. :) But good point about using wire of sufficient cross section.
    – Nobody
    Jul 1, 2017 at 17:52
  • The diagram I found indicated that only the 8 pin version has sensing pins. I don't know what your connecting via 6 pin pcie but assuming its a video card then 75w from the mobo and 75w from the 6 pin =150w max of your budget. Note the document says forced ventilation required at 160w or more. I would get a volt meter and monitor the voltage for several hours to make sure heat build up isn't lowering the PSU performance. I am guessing this is for a car PC, and if so then if the car gets 160 degrees on a hot summer day you could have issues and need 2 PSU.
    – cybernard
    Jul 2, 2017 at 17:36
  • the tolerance is + or - 5% max.
    – cybernard
    Jul 2, 2017 at 17:37

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