JUNE 2004 MAXIMUMPC 59
Is my 550W power supply really
consuming 550W at all times?
Absolutely not!
First off, a power supply’s rating refers
to its maximum output power rating
under ideal conditions. No power supply
is 100 percent efficient. In fact, some are
no more than 60 percent efficient—there
are some 550W PSUs that actually draw
around 800W to 900W in order to deliver
550W of output while allowing for the 30
to 40 percent that’s lost as heat, electro-
magnetic radiation, etc.
Thankfully, all power supplies used
in today’s PCs are of the “switching”
variety. Switching power supplies draw
only as much current as is needed from
the AC input. Therefore, when it’s only
required to pump 100W, the power sup-
ply is likely only consuming around
130W of power regardless of its maxi-
mum wattage rating. Feel free to get
the biggest, baddest PSU you can
afford. It will consume no more power
than a lesser unit.
What are sag and surge protec-
tion? Do I need them?
Before answering that, let’s quickly
define some terms. Sag occurs when
your electrical current drops. Ever turned
on a microwave oven and witnessed
your lights dim? That’s sag. Conversely,
a surge occurs when your electrical cur-
rent suddenly rises. High-quality power
supplies incorporate a multitude of
components to compensate for the brief
sags and surges in input power. In gen-
eral, capacitors help guard against sags,
while inductors and other components
help protect against surges.
These protective components help the
PSU provide your system with clean and
stable power even when your local utility
company feeds you the occasional hic-
cup. If you operate a backup uninterrupt-
ible power supply—a device that pro-
vides your system with several minutes
of backup power so you can save your
work in case your power goes out—your
PSU’s sag protection helps ensure that
your system has enough juice to run on
for the few milliseconds it takes the UPS
to kick in. Surge protection helps prevent
power spikes in the output power that
could tax your PC’s electronics, which
could result in instability and even per-
manent component damage.
You could get away with using a
power supply that lacks sag and surge
protection regulators, and you might not
even miss them. But it’s a gamble—are
you sure you want to roll the dice when
your PC is at stake?If I splurge on a quality power
supply with sag and surge pro-
tection, do I benefit from having
a redundant sag/surge protector?
Yes. It’s always a good practice to also
operate an external surge/sag protector.
Some of these units are likely to offer
much better protection against massive
power spikes (such as when lightning
strikes the electrical grid) than the surge
protection circuitry in your PSU, which is
designed to clean up modest fluctuations
in power more than anything else.
Furthermore, these external units pro-
vide protection to external peripherals
such as your monitor, scanner, printer,
etc, which don’t benefit from your PSU’s
built-in circuitry.What kind of fan should I look
for, or avoid, in a power supply?
One of the most common causes of PSU
failure is when the fan seizes up and
causes the PSU to overheat. Hence, a
high-quality fan is a great insurance policy.
In general, look for a power supply with
a ball-bearing fan. Ball-bearing fans are
more durable than traditional fans and
less likely to fail or get noisy over time.
They also cost significantly more than
their conventional siblings, so if a manu-
facturer includes one in its power supply
you can be sure it will be noted on the
label, packaging, and/or documentation.
Most new PSUs will also sport a connector
that allows the mobo to control the PSU
fan using the mobo’s temperature sensors.Is it true you can tell a PSU’s
value by how heavy it feels?
Yes, as a general rule, the heavier power
supplies tend to be better—remember
this when evaluating units from lesser-
known manufacturers. As for the PSU’s
innards, bigger is definitely better—beefy
capacitors and heatsinks usually distin-
guish the serious power players from the
poseurs. These items are also notoriously
weighty. So, suffice it to say, if a PSU is
feather-light compared with other units of
a similar rating, chances are it belongs in
the trash rather than your computer.What are adjustable voltage po-
tentiometers? Are they important?
A common misconception is that every
power supply outputs exactly 12V, 5V,
and 3.3V to each component as needed.
The truth is that they do not. Most mere-
ly deliver close to these specified volt-
ages with the deviation hopefully falling
inside the allowed tolerance of the ATX
specification. Sometimes the variation
is caused by less-than-spot-on toler-
ances of the PSU’s internal components,
while at other times it’s due to the power
source. Regardless of the cause, these
minor variations may be acceptable to
motherboard and chipset manufactur-
ers, but they’re far from ideal in the eyes
of a hardware fanatic. Some PSUs are
outfitted with adjustable voltage potenti-
ometers, which allow a user to fine-tune
output across a small range of voltages.
Also known as voltage pots, these
devices are not necessary, or even useful,
to the average PC user. However, serious
overclockers may find them useful for
improving system stability, and a valuable
asset when they’re trying to wring every
last MHz from an overclocked rig.Do different power supplies
offer different levels of CPU
and mobo support? How so?
Yes, there is more than one type of power
supply, and you must use only the type
of power supply that complies with your
motherboard’s formfactor.
The ATX formfactor has been the pre-
vailing standard for the past 10 years.
With the exception of mini-PCs and slim-
line systems, just about every consumer
PC uses an ATX power supply. It fea-
tures a 20-pin connector for the mobo.
However, recent leaps in power require-
ments by the leading CPUs have led Intel
to update the ATX standard to something
called ATX 12V. Dimensionally identical
to the standard ATX, 12V’s most notable
change is the addition of a four-pin 12V
connector for the motherboard. Newer
Intel and AMD mobos require this con-
nector to function. An ATX 12V PSU can
be used on an older machine, but not the
other way around.
Many current server and worksta-
tion motherboards, on the other hand,
require an EPS 12V power supply. These
have a 24-pin main connector and 8-pin
12V connector for the mobo. This is very
similar to an older PSU standard known
as WTX, but the pin assignments for EPS