Combine multiple voltage regulator?
You can connect multiple voltage regulators together but you are unlikely to get 200mA consistently from two 100mA voltage regulators. The main reason is the REG1 may be supplying 1mV more than REG2. With the outputs connected REG1 will tend to cause REG2 to shut down. It shuts down because it believes the output is slightly high and backs off the power.

Thus, in this simple configuration only REG1 operates with REG2 never contributing until the current limit of REG1 is reached then things get a little messy and unstable with a little bit extra noise on the output.

You can resistively connect the outputs of REG1 and REG2 and this alleviates the situation but, regulation purity is degraded and, due to the resistors, you will probably only be able to achieve 150mA from the pair. Resistor values of an ohm upwards are needed.