I have a 350W power supply and wanted to purchase the X1650 PRO video card for my system, but on the ATI website it says it needs min 420W. If I did put in that card, what would be disadvantage of having a smaller than recommended power supply.
With a graphics card its not so much about the total wattage of the PSU, The main thing you need to know is how many Amps you have available on your 12Volt rail as this is where the power for the card will be coming from. If your card wants 28 Amps and your PSU has 28 then you will be fine it dosent matter what the wattage of the unit is.
But basically there are about 4 main ways it could go if you try to run a card on a PSU that hasnt got the power to run it.
1 The card could run but at a reduced power/efficiancy so you dont get the full performance from the card, some cards will do this its called throttling back and they do it to avoid the damage that can be caused to the card by running it underpowered.
2 The card may just not run at all
3 Wont be a problem the card will run fine, manufacturers are usually very cautious and over quote the needed power to cover themselves
4 And this is the main reason why i say DONT DO IT . The card may go bang big time and take the rest of the computer with it.
Im not trying to be over dramatic or scare you it is a real possability that 4 will happen if you are not sure the psu will cope get a better one.
If your PSU doesn't supply the peak power the system demands during gaming, you will have instability (crashing and lockups).
X1650's are kinda power hungry. If you have less than 22 amp on the 12v rail with that PSU I would go with a different card. The 7600GS is typically about equal overall to the X1650 pro GDDR3 and uses alot less power. Even a 7600GT uses less power and it would almost always beat the X1650 pro. If you want ATI, then the 2600 pro would beat the X1650 pro and use less power.