PC Power Supply 5V Rating

[bobcat2000]

I am trying to upgrade my 460W Dell power supply.  I check the spec.  It has a 25A 5V rating.  So, I am trying find one that match the spec.
I found only one Corsair CX model that has a 25A 5V rating that was within my budget.  Many other brands only provide <20A 5V rating.

My understanding is that CPU runs on 12V nowadays.  The rest of the ICs still run on 5V (correct me if I am wrong.)

What make the Dell motherboard different that Dell requires a 25A 5V power supply that motherboards from other brands do not?

Thx!

[NiHaoMike]

Does it have a lot of USB ports (type A) or the capability to have a lot of SATA SSDs or HDDs? Those are the main 5V loads nowadays. In typical applications, less would be fine as long as you don't have too much stuff plugged into the USB ports. (Saw that problem with a development system that had a lot of smartphones plugged in for testing - machine would crash when deploying an app to many phones at once and the developers could not figure out why.)

[bobcat2000]

The Dell has 10 USB ports outside, 5 SATA, 1 mSATA, and 1 mini-PCI inside.

So,  I do need a P/S that can push 25A 5V.

Those 17A or 20A P/S won't cut it.

[Monkeh]

So,  I do need a P/S that can push 25A 5V.

Doubtful. Stick a clamp meter in there and see.

Why are you replacing it anyway?

[bdunham7]

What make the Dell motherboard different that Dell requires a 25A 5V power supply that motherboards from other brands do not?

Age?  What motherboard and CPU?

[bobcat2000]

It is a Dell XPS 8700 with a i7 4790.  The PS is very compact but draw a whooping 8A from the plug.  The Corsair CX may be too big in physical size.  May not fit inside the case.

[bdunham7]

It is a Dell XPS 8700 with a i7 4790.  The PS is very compact but draw a whooping 8A from the plug.  The Corsair CX may be too big in physical size.  May not fit inside the case.

Is it operable or broken?  If you can, I'd start measuring the actual currents rather than reading the labels.  I suspect your 5A needs aren't that great. 

[JohnnyMalaria]

According to: https://www.dell.com/community/Desktops-General-Read-Only/XPS-8700-Power-Supply-Replacement/td-p/4567328

This one: https://www.amazon.com/CORSAIR-CS750M-Certified-Modular-Supply/dp/B00GH9NA0A

[bobcat2000]

Oh!  You side tracked me.
I am not replacing the P/S.

I am wondering why motherboards from other brands don't need that much power.
The other MBs can use whatever.

[Monkeh]

Oh!  You side tracked me.
I am not replacing the P/S.

I am trying to upgrade my 460W Dell power supply.  I check the spec.  It has a 25A 5V rating.  So, I am trying find one that match the spec.

....

[JohnnyMalaria]

Oh!  You side tracked me.
I am not replacing the P/S.

I am wondering why motherboards from other brands don't need that much power.
The other MBs can use whatever.

But you started by saying you are trying to upgrade your power supply and that you have a Dell XPS 8700 

[wraper]

You don't need high current rating on 5V rail. Chasing for 25A rating on 5V rail is lame, such rating written on PSU does not mean that PC actually draws it. Actually when looking at cheaper PSU models, high current rating on 5V rail usually is a sign of crappy or prehistoric PSU since they also have low current rating on 12V rail.  Computers made in last 15 years consume little current from 5V rail, most of the load goes to 12V rail. I would be surprised if that PC draws more than 5A from 5V rail.

[bobcat2000]

Oh yea.  I said that I wanted to replace the p/s.  Must be Tuesday.  Can't remember what I typed.

[NiHaoMike]

I would be surprised if that PC draws more than 5A from 5V rail.

Budgeting 900mA per USB port and 1.5A per SSD (just looked at a random SSD in my collection, not sure how much peak current most draw under heavy I/O activity), it would not be hard to go over 5A at all. If the motherboard supports fast charging, that could be as much as 2A per port. (Note that USB-C with USB-PD uses a programmable voltage derived from the 12V line and does not load the 5V line at all.)

[bobcat2000]

USB ~ 1A
SSD ~ 1A
SATA HD ~ 2A

I have 10 USB ~ 10A
1 SSD ~ 1A
1 HD ~ 2A

13A + other chips like memory, chipset, sound chip, network, etc in the motherboard.

look like 25A is barely just enough if I hook up all the stuffs to SATA ports in the motherboard and the USB ports.

[wraper]

USB ~ 1A
SSD ~ 1A
SATA HD ~ 2A

I have 10 USB ~ 10A
1 SSD ~ 1A
1 HD ~ 2A

SATA HDD typically has <0.7A rating on 5V rail. Chance of populating every USB port with devices with such consumption is extremely low. You will need to populate every port with devices of high consumption, like charging smartphone, external HDD/SSD with no own power supply and similar. Not to say that as long as devices are within spec, they'll unlikely to pull such current.

In the USB 1.0 and 2.0 specs, a standard downstream port is capable of delivering up to 500mA (0.5A); with USB 3.0, it moves up to 900mA (0.9A). The charging downstream and dedicated charging ports provide up to 1,500mA

13A + other chips like memory, chipset, sound chip, network, etc in the motherboard.

Except most of it is not even powered from 5V.