Opio 330RS charger voltage

I travel with an HP notebook computer that has a 5v supply from its USB port. Can I use this to charge the camera (yes, the plug fits!) without overloading it? The camera is marked "DC in 4.5v" on the relevant socket. It would save me carrying yet another power adapter if I can do this.

I'd risk it. But then, I am a risk-taker.

G