will a 500 watt octigen dot he job or is octigen a dodgy company?
Personally... from looking at their website they look like rebrand whores. It's probably a cheap chinese PSU rebranded.
Put it this way, skimping on the PSU (especially a weird brand) could lead to things like fires / fried componenets or the machine turning off due the the rated power not being as specified.
Any power supply from here is considered "good quality"
http://www.overclockers.co.uk/productlist.php?groupid=701&catid=123
I would stick with Corsair as they have an excellent RMA turnaround should it go wrong.
Rob