Not NTD10 for S$4.475 la! Its NTD100 for S$4.475.
Anyway, our changi airport has always been very lousy compared to others. Taipei airport is the best, even their usual money exchanger outside have lousier rate than Taoyuan airport. But now currently is comparable to local singapore rate. No difference changing in taoyuan or SG here.
LOCALLY:
This is because SG rate is based on 3-4 months ago exhange rate and depending on the stock of currency they have - once depleted. They will replenish stock based on the current rate. Then depending how much, then the rate will fluctuate.
Then of course of they see the rate up in Taiwan, they charge abit higher - more profitable. If you are hardworking, go around and ask every single money exchanger, all different rate one and mostly difference in marginal like at most NTD0.50 +/-.
By the way, when local exchanger replenish their stock, they got it in a lump sum of millions of SGD - many dealers join in mah so they can get the best discounted current rate.