So, what's the 'real' wattage... Well, to start it off, the 'real' wattage is often referred as continuous wattage, which implies how much watts a PSU can be outputted continuously. Most generic PSUs (often referred as 'Cap Ayam' PSUs here) generally labels their PSU in terms of 'peak' or 'fake' wattage.
Those PSUs can deliver its labeled wattage, however they only last for a few seconds which is mostly useless.
But how do we know what's the 'real' wattage of the PSU? To answer this, you would need a load tester, and load their individual rails, and check whether the PSU is capable to deliver its labeled wattage without failure or not.
However, reading reviews of PSUs generally gives you how the PSU delivers its wattage.

If you have opened up your casing before, and if you take a look of your PSU, you will see something that look like this:

Well, that's the PSU label, which carries information regarding how many amperes on its individual rails.
So, what is a rail?

...er no, not that rail.
Actually, a rail (specifically in terms of PSUs) is essentially a voltage regulator.
But what are those +12V, +3.3V, -12V rails? What are their uses?
Those rails are powering computer hardware in your system unit.


+12V rail, the most important rail in modern PCs.... This is the integral part of the PSU, considering power-hungry components such as the CPU and GPU 'obtain' their wattage from this rail. A good PSU should have sufficient wattage on its +12V rail, and it should make up at least 80% of its labeled wattage. Apart from the CPU and GPU, the +12V rail feeds the main motherboard chipset, HDD and optical drive motors, most fans, watercooling pumps and the PCI/PCI-E cards.
But the question begins... How do I calculate the wattage on the +12V rail?
Well, by using the formula Power=Voltage x Current.
Here's an example of a Seasonic G 550 PSU.

From the PSU label, it says the +12V has 45A.
So by using the formula, 12x45=540.
That's 540W on its +12V rail.

But... how do I calculate the +12V rail of this PSU?

By using the formula, there 192W on its +12V rail, but there are 4 rails, so we multiply by 4,
192x4=768W ....or is it?

For multi-rail power supplies, the ampere stated for each 12V rail is their maximum current capacity, unless the stated ampere rating is not its maximum current threshold. For example, if each 12V rail in a multi-rail power supply has a rating of 16A, it means the maximum power it will be able to carry would be 192W ( again, considering if the stated ampere rating is the maximum for the rail ). It does not mean that the rail will supply up to 192W . If a multi-rail's power supply's 12V line has only 500W to spare to all the 12V rails connected to it, then they will have to ration the given power. The same applies for the 3.3V and the 5V line.

The same idea holds true for the +12 V outputs. On the power supply from Figure 29, each +12 V rail can deliver up to 16 A (192 W, or 12 V x 16 A), but the maximum combined power for the +12 V outputs is 504 W, not 768 W (192 W x 4).

So... the advice is, refer to the PSU label! They often contain important information about the wattage of the +12V rail.

What happens if you pull more wattage from its labeled wattage? More expensive PSUs however, will shut down as they have PSU protections configured. However, on generic units, they will fail, and may damage your hardware. This is the reason why the PSU should not be be skimped.
There are some other rails as well, however, I will not explain those rails for the sake of brevity. (will be explained soon)

In ideal conditions, the voltages on the power supply will produce a flat, horizontal line on the oscilloscope. However in real world conditions, that line isn't straight, they present some sort of oscillation, that is ripple.
Each ripple also presents spikes on the oscilloscope, called noise. ATX specs states that the power ripple should not exceed 120mV on +12V rails, and 50mV on +5V and +3.3V rails. Those values are peak-to-peak values. However, if the power supply can deliver its rated wattage without exceeding half of the maximum values in ripple, it is considered a top-notch PSU.
But the question is, how do I know the power ripple of the power supply? Well, you can't really determine them without using an oscilloscope, but you can read power supply reviews from reputable sites such as HardwareSecrets, TechPowerUp, JonnyGuru and http://hardocp.com/.

Voltage regulation.... The voltages on the outputs from the power supply must be as close to their nominal values as possible. In other words, we want to see the +12 V outputs delivering +12 V, not +13 V!

A little difference of up to 5% for the positive voltages or up to 10% for the negative voltages is tolerable. However, the voltage on +12V, +5V and +3.3V must be within 5% of its nominal values (+-5%)
What happens if voltage regulation, noise and ripple are out of ATX specs? You may experience...
1. Bad PC performance
2. Random crashes and freezes
3. ...and on extreme cases, damage your hardware!

This aspect is often overlooked; most users don't actually bother opening their PSUs to reveal the internals. However, some review sites such as HardwareSecrets and JonnyGuru. There are quite a bit of components inside a PSU, though for simplicity, I will be talking about the capacitor instead.
If you opened up your PSU, you will see something that look like this:

That cylinder-like thingy is the capacitor.
A capacitor is a small energy reservoir that stores a small amount of electrical energy. In terms of PSUs, they are used to smoothen the current of the output.
So, let's go to the main question.... Which capacitors are good in quality?
Generally, most Japanese-branded capacitors are good. Examples include:

1. Nippon Chemi-Con
2. RubyCon
3. Matsushita (aka Panasonic)
4. Hitachi

However, on lower-end PSUs, they often use Taiwanese or Chinese capacitors. Example includes:
1. CapXon
2. SamXon
3. JunFu
4. Fuhyyju (known to fail prematurely and they are found on older Antec PSUs)

But, does Japanese caps alone make a good PSU? No. In fact, some PSUs with Japan caps can perform poorly, for example the Gigabyte Odin Plus 700W.
Capacitors, however, don't do much on the PSU performance, but they help on the PSU lifetime. Good quality capacitors will help retain the PSU wattage over time.

Well, that was a pretty simple one. Branded PSUs are better. ...maybe not.
Yes, that statement is true to some extent, but do not attempt to stereotype them. Not all PSUs from a certain manufacturer is good. What we need to look at is the actual manufacturer of the PSU (will be explained later), and the reviews of the PSU.
Good PSU brands include:

1. Corsair
2. Seasonic
3. Enermax
4. Rosewill

However, do bear in mind that some units from those brands can be crappy, hence don't get blinded by the brand!

Apart from Seasonic, FSP and Enermax, most PSU brands don't manufacture own PSUs. They often rely on another manufactuer (the OEM of the PSU). Generally, common PSU manufacturer includes:
1. Seasonic
2. Super Flower
3. FSP
4. Delta Electronics
5. Channel Well Technology (CWT)

How to find out the manufacturer of the PSU? Again, let's take a look of the OCZ PSU again.

If you look closely, you will see a 'number' starting from the letter 'E'. That's the UL number. 'E130843' to be exact on the OCZ PSU.
If you key in the number in the website here,you will see something like this:-

From the picture above, you will know the PSU is made by Topower.
Again, don't be fooled by the OEM again, there have been some cases of some Seasonic and Super Flower-made PSUs performing poorly. Good examples would be:
Xion PowerReal 700W (Super Flower made) and Arctic Cooling Fusion 550RF (made by Seasonic, with same internals as the Corsair VX450 and the Antec Earthwatts 500W).

Phew, finally we arrived here. Now, let me talk about the efficiency, alright?
Efficiency is a measure of how much of the power a PSU draws from the wall actually reaches the computer. If a computer drains 400w, then an 80% efficiency PSU would theoretically draw 500w from the wall and the remainging will be given off as heat.
Refer to this diagram again for a clearer picture:

Credits to Phaedrus2401@Overclock.net

However, the PSU efficiency is not constant; it changes with respect to how much load on the PSU. Take a look at the efficiency graph of a Cooler Master PSU.

So, to make it clear, the PSU attains its highest efficiency at around 50% of the load.
That means should I get a PSU such that the peak draw is at 50% of the load? Nope in most cases
The reason behind it is because most of the time your PC is idling. However, there are some exceptions as well, for example, for those folding rigs.

80+ is an organization that tests power supplies for efficiency and a handful of other things (such as power factor correction, which we can ignore for now). 80+ has five certification levels: 80+, 80+ Bronze, 80+ Silver, 80+ Gold, and 80+ Platinum and 80+ Titanium (the latter not yet being attained in modern commercial power supplies). The higher the PSU's efficiency at certain load levels, the higher the certification level.

Credits to Phaedrus2401@Overclock.net

However, having an 80+ logo doesn't mean that PSU is good; it merely tells the consumer the efficiency, and it tells nothing about voltage regulation and power ripple.
Note that there are fake 80+ logos as well. Read here.

About Strike-X
The Strike-X PSUs are a series of PSUs with modular cabling (semi-modular, to be exact), with 80+ Bronze/Silver/Gold certification (The Strike-X 500M/600M isn't 80+ certified). They are available from 500W, 600W, 800W and 1100W configuration. The Strike-X is one of the highest end PSUs Aerocool can offer right now.

Verdict
Despite the eye-catching appearance, I can't exactly recommend the PSU, since the power ripple on the +5 output is exceeding ATX specs. The fan performance is less than impressive, as the fan is noticeably audible at full load. Even though it is priced around RM180 for a 600W variant, but it still becomes a hard recommendation since better, albeit lower wattage units (such as the FSP Hexa 500W and the Corsair CX500) may perform better. The 800W version becomes a hard to recommend unit at that price range as well, since much better units like the Rosewill Capstone 750W can be bought if you are willing to spend a little bit more.

Reviews
800W