Here is a very useful utility that will make your future customisations a lot smoother, this takes the headache out of choosing the correct PSU

http://www.jscustompcs.com/power_supply/

If you have any failing hardware then this might be a good place to start, check to see if your PSU is sufficient enough for your needs

This can come in handy , thanks Spellbyte :-)

Is there a program where I can see how powerful (watt) my PSU is?

It appears that the above power calculator is out of date

Here is one that has been kept upto date.

http://www.extreme.outervision.com/psucalculator.jsp

Nice one --garhar. Thanks. Bookmarked.