We update prices for all coins every 15 secs or every 1 minute depending on the exchange, so please allow for small deviations. If you feel that the coin price is far off from the price on the exchange:
First, check that you have selected the correct source and pair for the price.
In Delta, you can choose the sources of prices for each coin individually. The source of the same coin can be different in the Portfolio and in the Watchlist. For example, you could have XRP/USD, GDAX as the source of price for Ripple in the Portfolio and XRP/BTC, Binance as the source in the Watchlist. Check here to see how to select the source.
Second, sometimes exchanges like Coinspot also mention the fiat value and their way of estimating might be different than ours.
For example, with Coinspot, we use https://www.coinspot.com.au/sellallcoins as the source. Coinspot may be using the buy price or last known price to give their estimate of AUD value, which is why there might be differences.
For fiat estimates, we convert using Delta's global average values. Let's say a coin costs 0.005 BTC on Binance. We convert the BTC value to USD using Delta's global average BTC/USD rate (which will be slightly different from coinmarketcap's global average or Binance's estimation, etc.).