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1 2 3 4 5 NextMarch 21, 2008 by Mike
Chin
The SPI250EP appears at first glance to be a throwback to computer technology nearly a decade ago. What's a measly 250Wrated, genericlooking ATX12V power supply doing in a website for PC enthusiasts in 2008? Look more closely and you'll see the number "80" that's part of the 80 Plus logo, which identifies the product as a modern power supply >80% efficient at all loads from 20% of rated power all the way to full power.
250W rating and 80 Plus
tag make this ATX12V PSU unusual for 2008.
Most SPCR readers know about 80 Plus. In fact, an article about 80 Plus was posted on the front page just days ago. There are hundreds of 80 Plus approved, high efficiency power supplies. What makes this one special?
The vast majority of 80 Plus approved PSUs are rated for 300W or higher, the mean being somewhere over the 400W mark. This is significant if you're trying to achieve the lowest power consumption with very low power computer components: You're most concerned about the efficiency at 20% load.
A 400W 80 Plus power supply is assured to reach 80% efficiency from 80W (which is 20% of 400W) on up. What if your system only draws 30W? Chances are, that 400W PSU will do no better than perhaps 50~60% efficiency at this low output.
The efficiency vs power load plot of any PSU is a bell curve, similar to the efficiency curve of most machines. The highest efficiency is found typically at 50~75% of rated power. At maximum power, rising temperature makes efficiency sag, and as the load is reduced, the efficiency sags because the components and circuits are optimized for higher loads.
A 250W 80 Plus power supply is assured to have >80% efficiency down to 50W, compared 80W for a 400W model. This is the crux of our interest in the SPI250EP: It is the lowest rated ATX12V PSU on the 80 Plus approved list. We can hope that its efficiency doesn't fall off too fast below 50W.
Note expanded and limited vertical scale. The graph shows the relative efficiency difference at lower power for two PSUs that achieve the same maximum efficiency.

Are there many systems today that have <50W power demand?
There is a surprising high number of commercially available PCs that qualify as "Category A" desktops under the Energy Star Computer Specification v.4. There are 127 Category A models, defined as PCs that idle at 50W AC or lower, on Energy Star's Computers Product List  Desktops & Integrated Computers dated Feb 28, 2008. Based on what we know about a computer's power consumption patterns, when pushed to full load under real applications, most of these machines will demand no more than about 2.5X the idle power, which means ~125W peak. Apply the typical AC/DC conversion loss, and we're probably looking at peak power demand of perhaps 100W in DC.
For the doityourselfer, the number of component options for assembling low power systems is not small, and it's growing. Very low power CPUs that idle at just a few watts and max out at under 30W are available from from AMD, Intel and VIA. Motherboards with excellent integrated graphics for 2D work are both inexpensive and energy efficient. Even 3D performance is not bad with the latest chipsets such as the AMD 780G. A 2.5" mobile SATA hard drive of >300GB capacity that draws no more than a watt or two can easily take the place of the 7~12W 3.5" desktop drive. Basically, these are the same components used in some of the very low power Energy Star Category A commercial systems. The single biggest power bottleneck in such systems is usually the power supply, where upwards of 50% of incoming AC power can be lost, due low efficiency at such low output loads.
The unusual picoPSU with a high efficiency AC/DC power adapter has been the power supply of choice among ultra low power, silent system builders, as it can maintain nearly 80% efficiency even down to 20W loads. But it's not cheap and it has limitations, the biggest one being the difficulty of sourcing good AC/12VDC adapters rated for more than ~120W (if you want any headroom).
We recently identified and reviewed another Sparkle, the 80 Plus approved 220W SPI220LE, as a possible option for a high efficiency low power PSU. While not quite the equal of the picoPSU, it achieved 73% efficiency down to 20W and 78% at 30W, but its Flex ATX form factor makes it difficult for most DIYers to use.
So what are the main facts about this 250W PSU?

FEATURE
& BRIEF 
Our Comment 
ATX12V compliant.

Which version? Substantial differences between versions! 
Active Power Factor Correction (PFC) 
Required for 80 Plus. 
RoHS compliant

Required for sale in the EU 
Output over voltage, short circuit, and over current protection 
Standard
and required. 

The reason for our interest 
Approved by UL, CSA, TUV, NEMKO, CE

Standard. 
Universal
AC input range 100~264VAC 
Nice, fairly standard. 
Noise Killer (thermal fan speed control function) 
Standard. 
Dimensions (LWH) 140 x 150 x 86 mm / 5.5 x 5.9 x 3.4" 
Standard ATX 
OUTPUT SPECIFICATIONS:
Sparkle Power SPI250LE

AC Input

100264VAC; 4/2A;
60/50 Hz

DC Output

+3.3V

+5V

+12V1

+12V2

12V

+5VSB

Maximum
Output Current

14A

12A

8A

13A

0.3A

2.5A

106W 
204W 
Maximum
Combined Power

234W

16W 
250W

Maximum power ratings at 25Â°C working temperature.
Derate 1.5W/°C

A couple of notes:
 Stating that there are two 12V lines on a PSU that cannot deliver 18A total into 12V is just silly. The EN safety regulation this was meant to satisfy only calls for current to be limited to <240VA.
 The +3.3V and +5V line current capacity seems a bit high for an ATX12V PSU rated so low.
 The target market for the SPI250EP is not a DIY retail end user, but a commercial system integrator.
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