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Optiplex 790, PSU
You keep recommending the 700w PSU for the dell OptiPlex 790. That seems overkill considering that the PSU it comes with is 265w! I just need a PSU that actually works. So will and PSU be able to power 4 RAM sticks, a SATA III card, because for some reason the mobo has SATAII, and a GTX 1070.
speedstep
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July 31st, 2020 06:00
The specific models recommended have specific miniumum power output on the 3.3v/5v rails combined.
power supplies are not a single spec of WATTS. Units ihat have 90 to 130W max combined output for 3.3v/5v rails are insufficient. Dell has 142w to 225W on these rails. All Rails count.
EPS12v was revised several times due to increased power demand for 3.3v/5v combined as well as 5vSB.
EVGA 750B1 works fine but the B2 BQ N1 W1 G2 etc models from the same vendor do not work correctly for the same Power Rail related reasons. Dell in fact increased the power on the 5vSB and 3.3v/5v rails to over 30 AMPS and 225W.
All Rails count. You cannot use max power on all rails at the same time.
ihatedellandhp
14 Posts
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July 31st, 2020 10:00
The dell Optiplex 790 MT 265W in the picture above says
"+5V AND +3.3V SHALL NOT EXCEED 90W"
90 watts is less than 130 watts, which is what is the max on 5v and 3.3v rails on the EVGA 600W BR
IDK why you need the B1, the EVGA B1 lineup is unnecessarily expensive for no reason at all.
Again, people use the EVGA 450w on this exact computer, and IDK if they use a bus powered GPU or not, but if you use a bus powered GPU, do you need THAT SPECIFIC AMPEREAGE ON those rails?
Do you need that much PSU if you are using a discrete GPU with its own power?
ihatedellandhp
14 Posts
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July 31st, 2020 10:00
about this https://www.newegg.com/corsair-cx-series-cx650m-650w/p/N82E16817139148
ihatedellandhp
14 Posts
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July 31st, 2020 10:00
There are people who use an EVGA 450w BR, and a non bus powered card on this exact PC.
Im trying to get a card that is specifically PCEI connection powered
ihatedellandhp
14 Posts
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July 31st, 2020 11:00
Im not trying to use a bus powered card. Im only using a bus powered sata card, annd a PCIE 8 pin connection GPU. Will this work https://www.newegg.com/corsair-cx-series-cx650m-650w/p/N82E16817139148
speedstep
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July 31st, 2020 11:00
Tech Guide for 265w says max PCI-E card for the tower is 35W
https://www.dell.com/learn/us/en/04/shared-content~data-sheets~en/documents~optiplex-790-tech-guide.pdf
The other aspect you ignore is that PCI-E 2.1 and 3.0 use MORE 3.3v POWER per slot than PCI-E 1.0 or 2.0
PCI Express 3.0 changes specification in three areas: increased 3.3v power , performance and line code to 128b/130b vs 8b/10b encoding.
https://www.intel.com/content/dam/doc/guide/pci-express3-phy-implementation-considerations-idf2009-presentation.pdf