Is this a rip off??

Solution
I'd skip it because it's supposedly an OEM PSU but the actual manufacturer is not identified. It could be made by anyone including some guy who assembles spare parts in his garage. Always remember, "If it seems too good to be true it probably is!"
Possibly. If it's a genuine sale then no, it's certainly worth 15 of your dollars. Then again you might never see it...

I'm not familiar with what rebate is and why it'd knock 45$ off the price though.
 
It's an Ultra Products PSU.

It looks like it's based on an old design since it doesn't have Active PFC or automatic AC input voltage detection.

The OEM is most likely Andyson. In fact it looks exactly like the ANDYSON Advancement Model B Series 600W (AD-5620N2-36).
 
I'd skip it because it's supposedly an OEM PSU but the actual manufacturer is not identified. It could be made by anyone including some guy who assembles spare parts in his garage. Always remember, "If it seems too good to be true it probably is!"
 
Solution