PC power supply is, in many cases, attached just like an "accessory of chassis" when chassis is bought. In reality, it's no exaggeration to say that it is the most critical part of PC.
Because, to tell the work of PC mentioned above in one word, it is "to convert AC delivered to household and stably provide computer devices such as a motherboard" with DC (direct current). If it becomes unstable or broken, all functions get crashed to lose important data. 　

Is PC power supply special? No, No. In fact, many home appliances have power supply inside to convert AC to DC. Commonly seen AC adapter, for example, is externally placed type of built-in power supply. In daily life, we are not conscious of power supply of home appliances as it is built in them, and home appliances have no need to replace power supply because of no expandability of them.

Also, you cannot find out power supply for TV set at shops even when you want to replace. On the contrary, you may possibly replace PC power supply as PC has expandability to add HDD or replace CPU. Power supply is originally limited life component so that you need to replace at some stage.

<< Category and Differences of PC power supplies >>

First, take a look at dimension. AT type and ATX type have the dimension called PS/2 size. They may look identical. On the other hand, SFX type is less than 50% as small as PS/2 in volume. (Photo 2.1)
Each PC power supply has various shapes of main connector to be connected to motherboard and output voltages. This is because type of motherboard requires different voltages as shown in Table 2.1.

AT and ATX power supply are dimensionally identical, but there are much difference in its shape and output power to be recognized. Also, ATX power supply includes outputs of SFX power supply and its connector shape is the same.
For this reason, ATX power supply is available to mother-board of microATX. PC power supply is equipped with peripheral connector (large 4Pin connector) and FDD connector (small 4Pin connector) other than main connector. The shape and output voltages are the same despite the difference of number of connectors. (Photo 2.2 and 2.3)

Photo 2.2 Connectors of ATX type From left, main connectors (6Pin 2 pcs.), Peripheral connector, and FDD connector

Photo 2.3 Connectors of ATX and SFX type From left, main connector (20Pin 1pc.), Peripheral connector, and FDD connector

Fig 2.3　 For AT power supply, ON/OFF of PC power supply is controlled manually.
For ATX and SFX power supply, ON/OFF of PC power supply is controlled by signal from motherboard.

<< How to start up ATX power supply >>

Starting up ATX power supply by itself without connecting to motherboard can be carried out by giving pseudo signal.
This is useful to see where the problem that the unit does not start up comes from, power supply itself? or motherboard?
To make pseudo signal, turn PS_ON of main connector to TTL Low, or connect PS_ON to COM, providing that minimum load is given.

This is because just one transformer in PC power supply handles multiple outputs. Some units may not deliver 3.3V or 12V when 5V does not have approx. 2A of load.
Without any load, proper output may not be delivered when ON operation of power supply is carried out. Make sure to give minimum load. Many of our products can operate normally even with no load (zero amps.).

<< Is power supply which differs from the
specification of motherboard acceptable? >>

Some may wonder "ATX power supply is acceptable to motherboard of AT?" The answer is "YES."
Table 2.2 below shows the combination of different power supplies and motherboards to see what will happen.

*NOTE 1: Many SFX power supplies do not have -5V that is required by ATX specification. If motherboard requires -5V, the power supply is unacceptable, but some power supplies have -5V output. So it depends.
*NOTE 2: In the case that EPS power supply is connected to motherboard of ATX/microATX, conversion connector may be required.

Any motherboards are acceptable to ATX power supply.
However, in the case that ATX power supply is connected to AT motherboard, conversion connector from ATX output connector to AT output connector is required as they are different in shape.
In this case, ON/OFF control of power supply must be carried out manually as motherboard is unable to handle it.

<< How about compatibility between power supply and motherboard?>>

Often asked question is the compatibility with motherboard.
We do not know whether we can call it compatibility, but some power supplies do not work with some motherboards.

We are sorry to say we cannot check in-depth every combination of them to see which board is acceptable, and which is not. For ATX, strict specification has been issued mainly by Intel, but it has some degree of freedom causing some variance among manufacturers.
For example, suppose the following requirement that "PW_OK signal shall start up 100 to 2000ms after +3.3V and +5V reach 95% when power supply has started up. PW_OK signal shall start up within 10ms after it begins to start."
We need to follow this requirement that is "period from A to B", "Within C." Sole power supply meets this of course, but some power supplies may not work with some motherboards.
According to our experience as particular case, power supply did not work at specific rise time (dv/dt).

Also, the power supply works well with some motherboard, but does not with another motherboard even from the same
manufacturer.
Well then, can we solve the problem by eliminating the degree of freedom completely?
No.
The severer the specification is, the harder the materialization is resulting in higher cost and loss of customer's benefit.
Is the problem like this being solved?, or mounting?
We do not know, but we keep you updated with information in-depth.