PSU question???/

Do you have a question? Post it now! No Registration Necessary.  Now with pictures!

Threaded View
How can you tell if you are not getting enough power to your system?

I have a
Dell 8250, and it came with a ATI 9700. I recently upgraded
to the X800 XT PE. I
was just wondering if I was getting adequate
power to my system.

If not, can a
Dells PSU be easily upgraded? And if so, which PSU would
you suggest I purchase?


Re: PSU question???/

mroctober wrote:

Quoted text here. Click to load it

Check out:

Re: PSU question???/

On Sun, 27 Nov 2005 04:30:30 GMT, no@spam.invalid
(mroctober) wrote:

Quoted text here. Click to load it

You haven't told us anything about it, like whether it has a
branding or just "dell" on it, and the wattage (250W?).

Dell's PSU are far more honestly rated than some, else it
wouldn't have even worked with the R9700, and since you are
replacing that  card with one only a little more power
hungry, it'll probably be ok but you are likely pushing the
limits of the PSU and the ideal would be a larger unit.

Measure the voltages with a multimeter under heavy load,
like looping a gaming benchmark at moderately low resolution
(so CPU is stressed fairly too).  The multimeter is
necessary, software or bios readings of a voltage level will
not indicate a good or bad voltage level reliably.

If it turns out to be a problem, post the specifics of the
power connector pin #s vs their colors and any other
connectors used besides the 20-pin ATX going to the
motherboard.  It might be a standard PSU and if so, that
opens up a lot of possibilitites, while a proprietary unit
would have to be purchased at far greater expense from Dell
or (maybe) PC Power & Cooling.  The ideal replacement would
be spec'd for around 400W with at least 18A on 12V rail.

Re: PSU question???/

(mroctober) wrote:

Quoted text here. Click to load it

X800XT PE power stats are here. Click the graphic at the bottom
to see a magnified view.

5V@3.33A 12V@3.25A , 63W total from all rails.

Data is a bit harder to find for the 9700. This one gives 54W
for a 9700 pro, while running 3DMark2001. No details on
how this power was measured.

There really isn't enough data to make a guess as to the
impact of one card versus the other. From a total power
perspective, they aren't too much different. Depending on
how close to the limits the Dell is, on each DC output
rail, would determine whether the addition of a different
video card would "tip it over".

If the Dell had voltage monitoring capability, you
could see whether any of the rails are lower than they
should be. Basically, you look at the rails when sitting
idle in Windows, then have the monitoring software record
readings while you game. If big sagging is evident in the
collected data, that tells you the power supply is nearing
the limit for the rail in question (say +5V or +12V). That
is about all you can do, short of blindly replacing the
PSU with something bigger.

For a laugh, you can also try one of several power estimation
sites. This one breaks down consumption per rail, but doesn't
contain estimates for recent hardware. You can use some of the
data from this page as a baseline, then add in measured values
for hardware you find via other web sites.

Be aware that some of the power estimator web sites are
grossly wrong. Some memory power numbers are wrong by a
factor of 2 or 4. You can look up some real numbers, by
visiting sites like and downloading a datasheet
for a real DDR DIMM and getting the number from there.
Similarly, disk drive power numbers are available on the
manufacturer web site, if you want a reality check.


Re: PSU question???/

I just got off the phone with Dell, and he CSR told me that my PSU is
250w.  Anyway, it appears that my rig is running fine, but I just
wanted to ask here to see if I needed to upgrade.

Should I upgrade to a new PSU?

Here are my rig specs:

Dell 8250 2.4 ghz
768 ram    ATI X800XT PE (AGP)
120gb HD
PVR150 Audigy 2ZS Platinum
Logitech Z5300
Viewsonic VX924 LCD

Re: PSU question???/

  If that is the entire load, then the power supply is more
than sufficient.  Kony said, "Measure the voltages with a
multimeter under heavy load, ..."  Without numbers from that
measurement, then no one can provide accurate and additional

  That Dell supply at 250 watts may be equivalent to many
clone supplies rated at 300 or 350.

mroctober wrote:
Quoted text here. Click to load it

Re: PSU question???/

(mroctober) wrote:

Quoted text here. Click to load it

I can see it is a 850E based motherboard here: ?$=main/review/dell8250.htm

An 850E based motherboard. Pg.79 has a power estimate.

   Intel used these components in the following power estimate.

   1.7 GHz Intel Pentium 4 processor with a 256 KB cache
   128 MB PC800 ECC RDRAM
   AGP 4X/2X video card
   3.5-inch diskette drive
   11.5 GB IDE hard disk drive
   36X IDE CD-ROM drive

                          +3.3V  +5V   +12V  -12V  +5VSB
Windows 98 SE ACPI S0      2.6A  2.3A  1.5A    0A  0.3 A

Scratch the 1.5A on +12V. Recalculate the processor power.
Leave the 3.3V and +5V estimates alone, as we cannot separate
out the contributions of the various parts Intel used in
their measurement. My estimate might be 10W on the high side.

P4 2.4GHz/533Mhz Northwood. 59.4W 12V@5.5A at 90% efficiency

For 768MB via 4 RIMMs, 2x256MB + 2x128MB ? Takaman estimates
about 4 watts a piece, from +5V. Since I'm unable to find
any articles on how to calculate RIMM power consumption, I'll
have to leave it at that. (I have a datasheet for a PC800 RIMM,
but no industry standard formula mix for IDD1..IDD5)

Time to total them up:

                             +3.3V  +5V   +12V  -12V  +5VSB
Base mobo (overestimate)      2.6A  2.3A  ----    0A  0.3 A
Processor                     ----  ----  5.5A   ---- ----
Fans (estimate)               ----  ----  1.0A   ---- ----
4 RIMMs (conversion from +5V) ----  3.2A  ----   ---- ----
Hard drive (idling)           ----  1.0A  0.5A   ---- ----
CD drive (low RPMs)           ----  1.0A  0.5A   ---- ----
PVR150 (guess)                1.0A  ----  ----   ---- ----
Audigy (guess)                0.5A  ----  ----   ---- ----
X800XT PE (xbitlabs)          2.7   3.3   3.25   ---- ----

Total                         6.8  10.8  10.75   (whatever)
(Check label on side of PSU    ^     ^     ^
 for these current values )   /     /     /

Total power estimate - 205 watts. <--- This tells you, that
while the total power is not exceeded (250W supply), the power
supply is running at a significant percentage of its rating.
So, first check the three calculated current consumption
numbers, against the label on the side of the supply.
Chances are, the +12V output current is being exceeded.
Even if you are able to meet the three current numbers, the
supply is still getting a pretty good workout when you game.

Another thing to keep in mind, is there is a gross
mismatch between your processor and the video card. The
video card will not be working too hard, because the
processor will not be able to keep up. This will
ensure the video card operates somewhere between
the idle power numbers on Xbitlabs and the burn mode
numbers. Thus, it won't really be burning up
those 205W after all. Perhaps closer to 175W when you
run 3DMark or a 3D game...

Now that I know a bit more about your system, I think
you may find it benches about the same as with your
9700. And yes, I got burned like that once on a system,
bought the expensive video card, and found out I was
so CPU limited, it bought me nothing. Oh, the frames
rendered were a bit "smoother", but I was really no
further ahead than before. When you upgrade, sometimes
a lot of subsystems have to be upgraded to get anywhere.
Your motherboard likely is limited to a max of a
3.06GHz/FSB533 processor upgrade, so there isn't much
further for you to go with that motherboard.

I'd be interested if you posted a 3DMark score, with
the 9700 and with the X800XT PE, just to see if my
hunch is way off or not :-)

If you can find a shop that has a "clamp on DC ammeter",
they can measure power consumption for you. I own one
of those (cost me about $400 CDN at the time), and it is
handy for figuring out if the PSU is going to be OK.
It has some limitations on AC, though, and a Kill-A-Watt
meter is a better fit for measuring total wall power

(This is good for figuring out the power bill, but won't
tell you the breakdown of +3.3, +5, and +5V. A nice and
cheap meter, and used by some review sites.)

(This one clamps around the wires and measures the current
flowing through the wires. You don't have to cut any wires
or break any connections or anything. To measure AC in
an extension cord, you need access to the individual wires,
because the magnetic field around the hot and neutral cancels
each other out otherwise.)


Re: PSU question???/

mroctober wrote:

Quoted text here. Click to load it

A few years ago, C'T magazine measured the power consumption of systems
running AMD XP2400+ CPUs and NVidia ti500 graphics cards, and the
worst-case consumption was 190W.  Another person measured the power
drawn by his 64-bit Athlon 3000+ or 3100+ with a pair of 7200 RPM HDs,
a pair of 10K RPM HDs, and 1-2 optical drives, and it never reached
400W from the AC outlet, which translates into about less than 300W
from the PSU itself.

Some Dells use proprietary PSUs, others use standard ones, and the best
way to tell is by looking at the connectors.  A standard ATX 20-pin
power socket will have at least three orange or brown wires (+3.3V)
while a Dell-proprietary PSU will have only one orange wire (Power-Good
signal, but grey on standard ATX PSUs).  Unfortunately the plastic
connectors are identical, so it's easy to plug in the wrong type of PSU
and do some permanent damage.  Also those proprietary PSUs will have a
separate 6-pin socket with 3 blue-white wires for +3.3V power.  There
are adapter cables that allow a standard ATX PSU to be used in place of
a Dell proprietary one, such as this one:


Dell PSUs are well-built.  For example, here is "480W" Powmax Demon:

And here is a 200W Dell:

Notice how puny the heatsinks are in the Powmax and its high voltage
filter capacitors are only 470uF, the same size as those in the 200W

If you buy a replacement PSU, strongly consider something made by
Fortron-Source Power because they make very good ones that sell for
unusually low prices (, Some of their brands
are Fortron, Sparkle, Hi-Q, and PowerQ.

Re: PSU question???/

Dell uses PROPRIETARY power supply units.  I do not believe you can find a
more powerful replacement, though you would need one most likely for that
video card.


Quoted text here. Click to load it

Re: PSU question???/

DaveW wrote:

Quoted text here. Click to load it

As posted earlier:

Re: PSU question???/

I posted a score of 4437 in 3Dmark, with my new x800

I would like to thank everyone who has posted on this thread. I guess
I am stuck with what I got until I decide to do a complete Rig
upgrade (new purchase, with AMD)

I have been on many message boards and have come to the conclusion
that I need to do a complete makeover sometime over the summer of

Do you agree?

Re: PSU question???/

On Mon, 28 Nov 2005 03:30:28 GMT, no@spam.invalid
(mroctober) wrote:

Quoted text here. Click to load it

That's a fairly good score for your box but it's largely
because 3DMark now stresses video card far more than CPU.
In real-world gaming the CPU will tend to be a larger
bottleneck (on average) than  above score suggests.

That doesn't necessarily mean the card was a waste though,
if you like to play at high resolution and with all the
eyecandy turned up, it should help some.

Quoted text here. Click to load it

Maybe, though that's a fairly short use of the new video
card since the next system ought to be PCI-Express instead
of AGP based video.

Site Timeline