A normal 450W PSU (comes with cheap PC case) should be enough to run a normal PC - no OC, no high-end GPU. Just the matter of how well was it constructed in the factory. Some people can run it 24/7 for few years and it's still working, one of my friends unit blew up after 2 week usage...so it depends on your luck actually.

So if can afford a RM500 GPU, better use the money to buy a RM500 PSU first. Then save up again for the GPU. PSU is far more important than a GPU, although you can't play games in hi-res 1st.

Read an article in a Hong Kong PC mag, a guy's house was burned due to his cheap PSU power leakage. So, don't risk it.