If you just travel to Afghanistan, it doesn't matter what you bring, because all foreign currencies can be converted into local dinars, and you must declare them when you bring them into the Afghan customs. This can help you take out foreign currency, or use this voucher to exchange money at the local bank, but generally speaking, there are many channels for local exchange, as said upstairs, you can also exchange RMB for dinars.

There are no restrictions on bringing foreign currency into Afghanistan. You can take as much as you want, but remember to declare.