Using a USA charger in Europe I am about to buy an Apple charger on Ebay coming from USA, yet I am not sure if I can use it here in Europe, more precisely in Portugal.

I'm not concerned with the plug itself since I have the plug from my old broken charger and given that I can easily detach and attach it to the new charger this is not a problem.

My concern is related to the different electrical system used in USA and in Europe, so do I need to buy a converter or is it safe to use it ?

Best regards,

Filipe Silva.
If it’s a genuine Apple charger, you should be fine, those are universal. If it’s not (and it’s not unheard of for counterfeit items to be sold on eBay), all bets are off.

See for instance Ken Shiriff’s teardowns of iPhone chargers to see what enormous differences there can be among charger designs and their safety: http://www.righto.com/2012/10/a-dozen-usb-chargers-in-lab-apple-is.html