Two Higher Res Monitors on i620

I currently run two monitors - one Acer (P224W) @ 1680 x 1050 and one Dell (U2412M) @ 1920 x 1200 monitors with no problems. However, I want to step it up by replacing the Acer with a Dell  P2416D 2560 x 1440 monitor.

I am not gaming. My primary use is my Digital Audio Workstation.

Of course I want to run both at their maximum resolutions.

What do I need to do, replace the graphics card? If "Yes", I don't want to have to replace the power supply. Also, how do I know what physical size, etc?

Thanks for your help.

Thanks