Need info on which PSU to buy

What brand the 500W is? And 500W will be more than enough no worries.  

its a CiT, no idea what model it is though, as it hasn't got a PCI e connector for the HD7770 i deffo do need a new PSU. Here's the link to the case with the Psu i brought, http://www.amazon.co.uk/gp/product/B0064KJR6S/ref=oh_de... (sorry if links aren't aloud)

would this be good enough to power the everything and the HD7770 when i upgrade? http://www.amazon.co.uk/Cooler-Master-Elite-Power-Suppl...

The HD7770 uses very little power. A 380W Antec Earthwatts or 360W Seasonic "G" series is easily enough (either could handle a HD7850). Avoid the V2 version of the Corsair Builder; unlike the original Builder, which was made by Seasonic, the V2 (and later) versions are made by CWT, using inferior Samxon capacitors from a line known to experience early failure. Links provided on request. They review well, but won't hold up. Since I would not buy one, I cannot ethically recommend anyone else do so. The FSP "Raider" line is another good budget choice.

Edit: Absolutely NOT on the Crappermaster. It's a liar-labeled unit, and may be one of the ones missing protections. Here's the conclusion page on the similar 460W model: http://www.hardwaresecrets.com/article/Cooler-Master-El... . This kind of willful dishonesty (and most of their low-mid range PSUs are similar) is why I will never recommend ANY Crappermaster product, no matter how good. There aren't many in that latter category, although a lot of people like their cases and CPU coolers; fortunately their are also superior competitors in these categories as well, so you need not support a dishonest company.

would the Cooler Master Elite Power 500W that i put in my last post above be good enough?

NO! I edited my prior post. It's a liar-labeled piece of near-junk.

There are exceptions (e.g. the Crappermaster GX line, such as the 650W version, summarized by HardOCP as "a polished turd in a box"), but a quick and dirty rule for PSU selection is to get something that is 80+ certified. It isn't for the efficiency (although that's nice too), but for the fact it was run at 100% load. Although in a too-cool environment (23C), cheap Chinese junk PSU-shaped objects would die fiery deaths under those conditions. It says nothing about noise and ripple, or voltage stability, but in the absence of competent technical reviews (not consumer "review" fluff) it's about the only way to quickly weed out the worst of the junk.

I understand, i've been doing abit of searching, would this XFX PSU be worth buying? plus will it fit inside my case? http://www.amazon.co.uk/XFX-P1-550S-XXB9-PRO550W-Editio...

That's a good PSU; XFX PSUs are built by Seasonic. If your case takes a standard ATX PSU, it will fit.