The exchange rate between the US dollar and the Nigerian naira is constantly fluctuating. To determine how much a 300 USD Xbox Live gift card is worth in naira today, one needs to check the current exchange rate. Financial websites and currency exchange platforms can provide the most accurate and up-to-date rate.

When converting, it's important to note that the rate might vary depending on the source of conversion. Banks, online money transfer services, and even some forex trading platforms could have slightly different rates. This is due to factors such as transaction costs, market liquidity, and their own internal pricing models.

Moreover, economic and geopolitical events can also impact the exchange rate. For example, changes in interest rates, inflation levels, or political stability in either the United States or Nigeria can cause fluctuations. So, to get the exact value of the 300 USD Xbox Live gift card in naira today, it's advisable to look at multiple sources and consider the latest market conditions.