cx430M

Can I use a Video card rated for 450W with this power supply?

That is a very old power supply and should be taken out of service.

PSU has been in storage for 3 years. Low use. I will take it out of service when it dies or I need a bigger one.

And before that, it was being used.

It was discontinued over 6 years ago. And it had a three year warranty. So, it was out of warranty when it was put into storage, and sotred capacitors don't exactly age well. Unused capacitors actually AGE FASTER than used capacitors (Google "capacitor shelf life").

To ensure the PSU is going to work beyond it's six year age, you need to either replace the capacitors or do what's called "reforming" them (Google "reform capacitors").

Also, it's not a good idea to wait for a PSU to die in order to replace it. If a PSU has older capacitors, the capacitance decreases while ESR increases. This allows ripple and noise to pass more easily through the PSU and into your components where it causes further damage. So while the PSU seems to "power the components", it's also slowly killing them.

So.. yeah.. Unless you want to replace all of the capacitors in the PSU, don't use old PSUs.... ESPECIALLY if they've been sitting on a shelf for a long time.