I am assembling a power supply that requires a 12 V x 1 A. transformer. Among my components I found a 15 V x 1 A. Transformer. Can I use it?
You just need to check that the regulator circuit supports a higher input voltage. For example, if the regulating circuit can operate with voltages greater than that provided by a 12 V transformer, use is possible. This occurs in most cases, since a good tolerance is given in this type of circuit.