A transformer is a piece of electrical equipment that changes the quantity of energy that electrons have to a more pratical form. Obviously it losses energy when doing so as heat and reduces the quantity of current inorder to get the enrergy (energy has to come from somewhere). 1 volt electricity means that every electron has 1J of energy, 2.5V = 2.5J per electron and so on. Current is the flow of electrons through in 1 second (A). Charge is the total amount of electrons that passed in a given time (C). Do not quote me on any of this since I am still learning it.
Well anyway, a transformer exploding WOULD NOT fry your graphic card since the computers power supply is more lightly to to blow up before the card. Also if it did fry your Gcard, then your motherboard would have taken damage as well due to it opperating at an even lower voltage and current than the Gcard and thus is more sensitive.