Execpt that Raidmax (and other junk PSUs) are not rated for what they say. It may only be a roughly a 180~200watt PSU in the REAL world. It'll have very little amps to work with.
You can spend $20 on a 650watt junk PSU... and a $40 quality 300watt PSU from Seasonic will blow it away.
When the Video card makers say "400watt" they're trying to cover their "rear ends" for those with low-end PSUs.
While we can't say for certain that a new PSU will resolve your problems, your card being underpowered on a stressed out PSU could be running at a slower mode to prevent failure. If it was running full speed, your PSU (like other Raidmax) will blowup.
Go to
www.newegg.com: Look at Seasonic and Corsair as well as the brands Dustyjay says. Look at a 450~550watt model so that when you upgrade to a newer PSU, you'll have more to work with when you get modern computer with a more powerful video card.
Budget out about $50~75. And you won't be throwing good money after bad since the PSU will be reusable.