# Do PSU's draw full wattage always?

##### Distinguished
Right now my system runs fine with a high quality 600w PSU. If i were to buy a 1000w PSU for future upgrades, would it draw more electricity than my 600w, on the same setup, or is the extra wattage only there in case something needs it?

Solution
The fine detail on what you ask is that the % Efficiency rating for most PSU's is not the same for all power levels - it may be 80% at 75% of maximum output, but it will vary from that at other power outputs. HOWEVER, the variation is so small over any reasonable range (say, from 25% to 95% or max output) that you really do not need to worry about it. In your case, check the % Efficiency rating of the PSU you already have, and of the new larger one you are considering. If they are the same then the new one will use exactly the same power as your old one until you change your other system components. And if you can get a new larger unit with even better % Efficiency, you'll actually come out ahead of the game.

#### saaiello

##### Splendid
It will run the same since it will only draw what it needs. Now the need for a 1000 watt PSU is not really needed do you have a reason you want a 1000watt PSU.

#### shubham1401

##### Distinguished
Suppose, if your system needs 300W of power. Then no matter if you use a 600W PSU or a 1000W PSU it will furnish 300W of power.

But If your system is a power hog and needs 700W power. then you need a 1000W PSU to supply that much of power.
That's when you need a 1000W PSU.

So, if your system runs fine with a high quality 600W unit then you don't need to buy a 1000W.

#### Lmeow

##### Splendid
Well, no, as the other two have said. If your system components only use say 250W and you have a 500W, the system components will only use 250W. However, say that the PSU's peak efficiency @ 50% load is ~90%, then, it would take around ~275W from the wall.

##### Distinguished
thanks. 1000w was just an arbitrary #. If i ever decide to try and crossfire one of these new graphics cards i'll definitely have to upgrade my supply, so i was just thinking of doing it now if i saw a good deal somewhere.

#### shubham1401

##### Distinguished
What are your system specs?And which PSU do you have?

Some cards will CF on a 600W PSU !

A quality 850W Can handle most of them.

#### Paperdoc

##### Polypheme
The fine detail on what you ask is that the % Efficiency rating for most PSU's is not the same for all power levels - it may be 80% at 75% of maximum output, but it will vary from that at other power outputs. HOWEVER, the variation is so small over any reasonable range (say, from 25% to 95% or max output) that you really do not need to worry about it. In your case, check the % Efficiency rating of the PSU you already have, and of the new larger one you are considering. If they are the same then the new one will use exactly the same power as your old one until you change your other system components. And if you can get a new larger unit with even better % Efficiency, you'll actually come out ahead of the game.

##### Distinguished

Mobo: MSI 790FX-GD70
BIOS: 1.9
CPU: 955 BE @ 3.8g
RAM: OCZ AMD Black Edition 4GB (2 x 2GB) 240-Pin DDR3 1600 SDRAM DDR3
Vid: HIS iceq4 turbo 4870 1g (790mhz gpu, 1100mhz memory)
PSU: COOLER MASTER Silent Pro 600 RS-600-AMBA-D3 600W
HDD: SSD - OCZ vertex turbo 60g, 140g raptor
OS: win 7 32 bit

I was looking at the new directx 11 cards, and the high-end ones (5870) seem to draw a LOT of power

#### shubham1401

##### Distinguished
Actually 5870 will run easily on your PSU.
But if you want to CF then do consider a bigger unit

thank you