You could also look at this is as if the exporters got fair market exchange rates for the USD they earn, and the government took some of the pesos the exporters were given, and immediately converted them back into USD. The effect is the same, as the exporters end up with less money than they earned, and the government pockets USD.
Overall, this reduces the resources available to people holding (the same number of an increasing pool of) pesos, thus devaluing the currency.
The fixed official exchange rate also allows for less obvious increases in the money supply (inflation).
So, the open market value of a peso is about 0.10 USD. The official value is 0.15USD.
The official value of 1 peso (0.15USD) is higher than the open market price (0.10USD). Thus the government is overvaluing the peso.
In contrast, 1 CNY is currently worth (0.17USD), i.e. similar to the official value of 1 peso. However, some people argue that it should be worth much more (e.g. 0.25USD).
In your example, exporters are getting screwed through an implicit tax. In my example, exporters are getting an implicit subsidy.
Exporters use USD (which they receive from overseas buyers) to buy CNY. Those USD add to China's foreign currency reserves.
Source:
http://people.hofstra.edu/geotrans/eng/ch5en/conc5en/yuanusd...
RMB was trading 1-1 with the dollar in '81, and started getting real about it in '94.
Argentina, obviously, produces some high quality goods but in another scale.
The government is taxing exports by underpaying exporters for their goods, while collecting market prices from the foreign customers. The government achieves this by overstating the value of the Argentinian peso, which the exporters are forced to accept as payment (at government dictated exchange rates). This would be a problem if the government allowed citizens to purchase USD at the artificial (low cost per USD in pesos) price, so the government restricts USD purchases in Argentina.
The Chinese government implemented this policy before Argentina, which is why they are always accused of manipulating their exchange rates.