Basic question about power supply

[TThomas]

Hi,
Sorry if this is a stupid question but electronics is not exactly my strong point!
I have a Netgear router with a power supply with the following specs:
Input: AC 100/120V 50/60Hz 0.5A
Output: DC 12.0V 1.5A
I need a 220V power supply and want to use the one that came with my Vonage ATA, the Dlink VDV21-VD. The specs are as follows:
Input: 100-240V 50/60Hz 0.8A
Output: +12V 1.5A
My question is the 0.8A input as opposed to 0.5A a problem?
Also the model number of the Dlink is DSA-18W-12. I assume that means 18 watts. If so is that a problem.
Thanks
P.S. I would appreciate an explanation of the answer so that I could learn a little about this topic.

[Biffo]

If you use half the voltage then you need double the current (and therefore thicker cables)

so say something is rated at 120 volts 1 amp
in its 240v form that would be 0.5 amp