Thevenin equivalent, of circuit with one voltage and one current source
The current source does not affect this circuit at all.

The voltage source forces a particular voltage across the nodes the two sources share. If the resistors and the load connected between a and b do not sink 1 A with 10 V across them, then the voltage source will sink the excess current. 

This of course only strictly applies to the theoretical circuit using an ideal voltage source. 

Many real devices that we might crudely model with a 10 V source can only source current but not sink current (Other kinds of voltage source, like shunt regulators, can only sink current).