HELP Please! Want to upgrade Video & PS on Dell 435mt...Best PS and VC

Hi all,
My stock Studio XPS 435mt from Dell has a very low wattage PS and I want to upgrade my video card Radeon 4800 (which I cannot even upgrade the drivers, having to use old ones from 2009 as new ones cause power problems and not approved by Dell as usuable).

Can Anyone suggest the best power supply to upgrade to that fits well and keeps the system cool?

Can I ask for specific Models of Power Supplies as seen may threads stating upgrades to 600w or 700w PS but don't state specific model numbers or types.

Also what is the best Video card to swap out? Am playing SWTOR and have to set down setting to Good now with 4800 and older drivers.

Thanks,
Don