Does PSU automatically take required input?

I have the same PC config as a Core i5 2400 3.1Ghz,Intel DH67BL,4GB RAM DDR3 1333Mhz(2x2GB Corsair,Kingston),1TB Seagate 7200.14 HDD with no add-on cards.For some days I am not going to "play" graphics intensive games like Call Of Duty series,Crysis,Assassin's Creed series etc.So I took graphics card(XFX GT 240 1GB GDDR5) from PC and kept in it's box with electrostatic bag and silica gel and I hope it will remain in good condition for a long time.By the time,I use Intel HD Graphics 2000 Series and I think it will be sufficient for my current activities which include just watching HD movies and playing "chess titans" and "minesweeper".Why I did this becuase I just need to save power.
Now the problem:
Core i5 takes 95W maximum with Intel HD 2000 series.Noway I am going to utilize the full power of it and most of the time,it will operate at half of original frequency i.e 1.5Ghz(approx).So we can say it can utilize maximum 70 or 80W.Now with 1 HDD,1 DVD Writer,oboard LAN-USB-Audio enabled but USB 3.0 is disabled since I have no such device.So.
Processor-80W
Rest- 30W(just saying)
So all together - 110W or maximum 125W if processor is fully used.But my PSU is Antec VP550W series.My question is though the system components take maximum 125W,then PSU will supply the same power?I mean 125W and NOT 550W(70-80% efficiency,so 412-440W approx).Does PSU supply only needed power?
Saving a 70W is really a great thing for me since I use a table fan of 70W daily:)

Yes, the PSU is only drawing power that it needs. My question is why? This may be one of the most paranoid power-saving steps I've ever heard of.

The cost difference in running your PC with onboard graphics versus the add-in card is most likely going to be around $1.00 a month or less.

Put the card back in your computer, and enjoy using it. Spend your efforts worrying about something more important!

I just want to know about this.The card is an XFX GT 240 1GB GDDR5 and takes up to 70W maximum.However the card has 3 power management levels -> IDLE(GPU CORE CLOCK:135Mhz,GPU MEMORY CLOCK:135Mhz and GPU SHADER CLOCK:270Mhz)<2D(405Mhz,324Mhz and 810Mhz) <3D(550Mhz,1700Mhz and 1340Mhz).
Does the power consumption depends on the LOAD or these levels?
For eg:If the card is at full frequency i.e full speed at 3D level but the load is minimal such as <10%,then does it mean it consumes 60-70W?

I'm still not sure why you're putting so much effort into it. You aren't going to be saving a measurable amount of money.

Usually, newer cards have power-saving modes that the card goes into automatically. They draw far less power when you are viewing a webpage as opposed to running a game. The power it draws will depend on many factors, and isn't just some number that can be found by an equation. It will be dynamic. If you really care what your system is pulling, get a UPS, such as an APC that will give you software to monitor the load.