The +12V output is very important in PC power supplies because the CPU and VGV both require a +12V input. The +12V output can be subdivided into a single +12V rail and multiple +12V rails.

1. PC Power Supply
+12V distribution

2.  The +12V output is very important in PC
power supplies because the CPU and VGV
both require a +12V input.
 The +12V output can be subdivided into a
single +12V rail and multiple +12V rails.
+12V distribution

3. The single output is mainly used for a single device whose
maximum power consumption may exceed the 240VA limitation
(which may trigger Over Current Protection, OCP) or when two or
more power-intensive devices cannot be effectively distributed
among multiple +12V rails, a single rail with a large output is then
required.
Single +12V rail

4. Single +12V rail
Advantages:
1. Mainstream design.
2. Compatibility issues rarely occur.
3. No power dispersion on power distribution.
4. Without current protection, problems almost
never happen.
5. No need to keep track of which devices are
connected to which rail.
6. Makes cable connections easier to manage, and
you generally need fewer cables so you can keep
the case neater.
Disadvantages:
1. Insufficient power can become significant when
using high-power devices.
2. Even with the OCP, the direct output current
may still damage components.
3. A single +12V output will be significantly
affected when the output is unbalanced.
4. In the event of a short circuit and the power
supply responding slow, the shorted component
may be burnt.
5. In prolonged high or full load work conditions,
both the heat dissipation and power conversion
of the power supply will be unsatisfactory,
power tends to be lost, and the service life will
be shortened significantly.

5. The purpose of multiple +12V rails is to prevent
excessive voltage drops caused by a single high-power
device that affects operation of other devices.
Each rail is limited for a maximum output of 240VA (no
more than 20A in the case of 12V).
Multiple +12V rails

6. Multiple +12V rails
Advantages:
1. No insufficient power even when using high-power accessories.
2. Each +12V rail has independent short circuit protection, providing a complete safeguard.
3. Two independent +12V outputs will only affect each other to a minimal extent under
any conditions.
4. Splits a single +12V source into multiple +12V outputs, with each wire having a limited
output current. This makes the circuit configuration safer.
5. Since the power supply works at (relatively) low-load conditions most of the time, it
greatly helps with heat dissipation control or integral conversion efficiency, thus service
life of the power supply is therefore prolonged significantly.
6. In the event of a short circuit, the power supply will react quickly to cut off the power,
therefore protecting system components.
Disadvantages:
1. Standard accessories in the case rarely require multiple +12V rails.
2. Distribution of the multiple rails must be designed carefully so as to prevent excessive
over current protection.
3. The load of each rail must be able to be read to have a comprehensive understanding of
the power output. If rail splitting is poor, wasted wattage will occur.

7. Which one is better?
In current multiple rail switching power supplies,
the difference between a single large output rail
and multiple small output rails is only in the setting
of output distribution. For general applications,
single rails differ little from multiple rails. However,
for users with high-end CPUs, CPUs with
compressed overclocking functions, or dual CPU
platforms in combination with high-power single
or dual VGA cards, using a high-output single rail
power supply can minimize disturbances from OCP
activation due to the output limitations and poor
circuit distribution of multiple rail configurations.

8. Which one is better?
In summary, the single +12V rail is more
economical and easier to use than multiple +12V
rails. Therefore, it’s more common to find the
single +12V rail power supply in the end user
market.
Multiple +12V rails provide more comprehensive
protection than a single +12V rail. System
Integration will more tend to bundle the Multiple
+12V rails power supply in the system.
In fact, they all have their pros and cons. As for
which one is the better choice, it all depends on
what the user’s requirements are.

9. ERN Series
Available
Wattage
300, 350, 400, 450, 500, 550, 600W
Dimension 140mm (L) × 150 mm (W) × 86mm (H)
General
Specification
Efficiency Level 80PLUS Sliver
Erp Lot <0.5W
Input Voltage 100~240Vac
Efficiency
85%@ 20% load; 88%@ 50%
load; 85%@ 100% load
Output Voltage
+3.3V +5V +12V -12V +5Vsb
300W 21A 15A 24A 0.3A 3A
350W 21A 15A 28A 0.3A 3A
400W 24A 14A 33A 0.3A 3A
450W 24A 15A 36A 0.3A 3A
500W 24A 20A 39A 0.3A 3A
550W 24A 22A 42A 0.3A 3A
Model Available - Single 12V rail ERN Series

10. EGN Series
Available
Wattage
400, 450, 500, 550, 600W
Dimension 140mm (L) × 150 mm (W) × 86mm (H)
General
Specification
Efficiency
Level
80PLUS GOLD
Erp Lot <0.5W
Input
Voltage
100~240Vac
Efficiency
90%@ 20% load; 92%@ 50% load;
89%@ 100% load
Output Voltage
+3.3V +5V +12V1 +12V2 +12V3 +12V4 -12V +5Vsb
400W 16A 16A 18A 18A - - 0.3A 3A
450W 16A 16A 18A 18A - - 0.3A 3A
500W 16A 16A 18A 18A - - 0.3A 3A
550W 16A 16A 18A 18A 18A - 0.3A 3A
600W 20A 18A 18A 18A 18A 18A 0.3A 3A
Model Available - Multiple 12V rail EGN Series

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