Upgrade stock PSU (Dell 530 Inspiron w/ 300 watt PSU)

Okay guys I have a Dell 530 with these specs:
Computer is 1.5 years old
Vista 32-bit
E6550 core 2 duo
HD 2600XT
4 sticks of RAM (1GB each)
1 7200 HDD
1 DVDRW
PSU is the 300 watt version. Looking online it appears to have 18A on the 12+V

I play these games:
Anno 1404
Age of Empires 3
Settlers 2 10th anniversary
TW: Medieval 2

Resolution 1680 x 1040

I have two questions:

1) If I replaced the HD 2600XT (which came stock on the PC) with a Radeon 4670 or the PNY Gefore 9800 GT EE do I even need to upgrade the PSU?
2) If I should upgrade the PSU what do you suggest?

How many threads about this Dell do you intend to start today?
That PSU is not 80+ certified, so I would not buy it. Get an Earthwatts 380 if you want to upgrade your PSU.
And, PSUs with 120mm fans (or larger) are usually portrayed up-side down. Normally the PSU mounts with the fan facing down into the case (in cases where the PSU mounts on top); it can be mounted up-side down if desired, for example in cases where the PSU is on the bottom.

Which one of these would you suggest for the ~$50 or less range?

http://www.newegg.com/Product/Prod [...] 6817182160 41Amp -$55
http://www.newegg.com/Product/Prod [...] 6817341017 42Amp -$55
http://www.newegg.com/Product/Prod [...] 6817139008 30AMP -$30
http://www.newegg.com/Product/Prod [...] 6817611007 46Amp -$50
http://www.newegg.com/Product/Prod [...] 6817611008 54Amp -$50

And which card would you suggest for $100 or less?

Basically if I bumped my budget up to $150 for a new card and PSU what would be the best investment?