What's the best possible psu brand i can buy that's under $100

Both cards are ok but the 4770 is faster by a fair margin, but watch what you pay, the even faster HD4850 can be found for the same price, or less if you shop carefully.
Assumung you do not have a multi-CPU server or a dozen hard drives 400-450W from Corsair, Seasonic, Antec, Pc Power and Cooling or OCZ would be more than enough (go for the 450W if you buy the Hd4850).

So it really doesn't matter what type of psu i buy as long as it reaches the minimum requirement for the Watts.

No.
Stick to a good brand, like those I mentioned, cheap power supplies may only be able to provide a fraction of the power they claim and they lack protection, meaning if it does fail it can seriously damage the sytem.
This is nice:
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

Or for a few dollars more you can go way over the top:
http://www.newegg.com/Product/Product.aspx?Item=N82E168...

I still have one more question, what is the DX11 I've been hearing about and people waiting to buy graphics cards when that comes out, if i buy a graphics card when that comes out will i not be able to play with new games or something or can i update my drivers to DX11. I'm kinda confused.  

Do n't worry about it, but take a look here, it gets a bit technical at times but should answer your question:

http://www.tomshardware.co.uk/forum/page-266672_15_0.ht...

1. listen to the Cooz, don't go with a ceap power supply. A lot of them give false test readings so the watts they display you will not see in real world scenarios. Antec, OCZ, PC Power & Cooling, and Corsair all have good PSU for under $100 that will meet your needs.
2. directx11 is part of windows 7
http://en.wikipedia.org/wiki/Direct3D#Direct3D_11

3. If you buy a graphics card now you can still play the latest games and even newer ones that come out since they will be able to run on XP and Vista. If you don't plan on upgrading to windows 7 in the foreseeable future then you don't need a directx11 card right now. If you do plan on getting it soon after its launch, then holding out until the new cards may be a good idea.

http://www.newegg.com/Product/Product.aspx?Item=N82E168...

Alright so back to my original question, i bought my psu for 90 bucks and the ati radeon 4670 for 85 bucks   . The brand of my psu is rocket fish and has 550 watts. I couldn't find the brands mentioned above because unlike other people I buy my things at stores like staples and best buy(but that's not the problem). Now when i installed my psu and the 4670 it seemed like my PC started OK but the fan or something that you hear humming from the computer got just a little bit louder. I started playing Mass Effect(pretty awesome rpg) an hour and half later and my pc randomly shut off.  

I'm not sure why it shut off but I'm assuming it's from my new psu. I'm pretty sure that I installed the wires correctly and cleaned the dust well from inside the computer. Hint Hint notice i said pretty sure that I installed the wires correctly so not 110% but 80-85%. But seriously could it be that the 4670 might have a tiny bit effect on this, or something else like my motherboard or is it the psu i installed. Please post some ideas and i might run through some other things i might of need to do or receive help from.Thanks  

check to see the cpu fan and all the case fans are plugged in

download hwmonitor too see what temps your CPU and GPU reach during gaming

Dude that's a beast program, but now i'm kinda scared   because i'm assuming that 45-55C isn't good for my temperatures and that's what I'm receiving now. What to do know

i accidentally double posted

EDIT: the earlier post was without gaming, but when playing Crysis on Mainstream settings the temperature in GPU went up to a max of 78C.

45-55C for an idle card and 78c under load are normal temps