> The way this normally happens, USD deposits are made to an exchange that has a relationship with Circle, and 1 USDC is minted for each 1 USD on deposit at Circle.

On the other hand, the most popular (?) stablecoin, Tether (USDT) doesn’t have a one-to-one relationship with USD deposits, and the amount it really has in USD is believed to be very low (I don’t know the numbers, but have read that there haven’t been any audits or published audits).