(Q) the new "xyx" motherboard has a 24pin plug - so do i need a new 24pin PSU ?
Not necessarely. All the upcoming new boards (eg. Nforce 4) SHOULD be capable of running with an "old" ATX 1.3 20pin-plug equipped PSU as well as with a new ATX 2.0 24pin PSU.
The question here is rather whether the PSU itself is a good brand name PSU with sufficient wattage. Dont expect a recent high-end system with pci-express card(s) and A64 CPU to run flawlessly off an old 350W noname PSU.
(Q) but what about the extra 4 pins on the PSU plug/motherboard connector ?
These four extra pins on the newer ATX 2.0 PSUs are solely for providing power to the pci-express port . I guess the specs demanded a separation of the power-rails for CPU/motherboard and high-end graphics.
Therefore they put the additional rails on the plug/motherboard which provides +12V, +5V, +3.3 and GND to the pci-express slot.
(Q) So..but i got/plan to get a pci-express card !
pci-express cards will MOSTLY have an external power-connector (6 pin pci-express). You can connect two unused molex connectors from your PSU to this connector on the graphic card via an adapter. If you dont have this adapter - newegg has one
pci-express power adapter
(!) a single connector/wire on a PSU/connector is usually rated at a max. power draw of 6A. Wattage = VOLTS*A.
The maximum wattage for ONE 12V connector is therefore 72A. The two molex connectors are combined since a high-emd graphic card usually uses MUCH MORE than 72W..therefore it uses two molex which should be ok for up to 144 Watts.
THATS why the pci-ex graphics card SHOULD be able to run fine even WITHOUT the 24pin motherboard connector and WITHOUT a newer PSU with 24pin plug. The card gets enough power already and does not REALLY need the power from the PSU plug.
Thats why the newer boards are USUALLY comaptible with either 20pin PSUs or 24pin PSUS.
[As a sidenote] A pci-express card with NO external power connector which would get the power solely from the pci-port can (therefore) only draw a max. 72W. The current high-end cards all draw much more power. Eg. a Geforce 6800 Ultra is listed as using as much as 110 Watts. There is no way to do this with just the power coming from the 6A/72Watts rated pci-slot
(Q) But wouldnt it be just better to get a newer ATX 2.0 24pin PSU which is "pci-express ready" ?
First..."pci-express" ready is just a stupid market term. See above. It doesnt need to bother you if the graphics card has an external connector and you got a good strong 20pin PSU.
"pci-express ready" will usually only mean that the PSU will have a 6pin pci-express power plug. Which is not bad and saves you the hassle to get the adapter in case the card does NOT come with one.
Another advantage of the newer ATX 24pin PSUSsis that they USUALLY have dual, separate 12V rails. (One 12V rail provides power for eg. CPU, the other rail is separate and provides power for the pci-express card.)
This is not necessarely bad
In other words: You cant go wrong with a new 24pin PSU for various reasons. But this does not mean that your older 20pin one is obsolete. Especially not if its a good brand name one with suffcient power.
(Q) I got a 20pin PSU and i will get the "xyx" motherboard which uses a 24pin connector. So...i can get one of these PSU "20pin -> 24pin adapters" to make my old 20pin PSU 24pin compatible ?
See above. I dont THINK you really need one. But..there are certain *concerns* regarding this "20pin to 24pin" adapter. Do NOT confuse with the "24pin -> 20pin" adapter which often comes with new ATX 2.0 motherboards.
The 20pin->24pin PSU adapter will split your ONE rail/wire (eg. the 12V rail) coming from your PSU in two and create the "artificial" extra 4 pins.
The result is that your PSU will draw much more power from the one rail than it was originally intended to. While a real "dual rail" PSU will provide two seperate rails the solution with the adapter will draw twice the power now from one 'wire'.
What was rated at 72W max. before (remember ? 6A * 12V = 72 W) will now all of a sudden draw up to a max. of 144 watts.
Also..the thermal load (eg. heat !) will increase 4 (four !) times.
The most strain wil be on the adapter/plugs itself. You will get some nice, hot wires and plugs...
I cannot see this as an elegant solution - HOWEVER it might work.
But remember: You probably wont even NEED the adapter.
