How much power (in watts) can I get from my house outlet?
Don't put the AmMeter's probes in your outlet! Never! You are right about the BOOM :)

1) The local electricity company when connected your home made a design and gave you some reasonable allowed maximum power. It can be 5kW, 6kW, 10kW... depending on house size and local regulations. Find your contract and this information should be stated there. If you have no contract call and ask them. This is your legal limit.

2) In the way of the electicity to your home there are circuit brakers. Usualy they are rated for about 50-70% more than the power by your contract. A circuit braker may be for 32A, 50A, 63A, an so on. This (+some % overrating) is the maximum current you can draw from all outlets in your house at a same moment.

3) The wires that go from the circuit breaker to your outlet are calculated upon a prediction for a maximum current that will be drawn by this particular outlet. If you draw much more current for extended period (hours) the wires may heat up, melt isolation, accidently make short circuit and produce fire. A wire's current rating depends mainly on its cross section, but also on type of cable and how it is been layd in the wall, whether the wall is concrete or wooden and so on.

People study 5 years engeneering to design electrical installations. This cannot be explained in a few lines.

The benefit of 220/230/240V is that at a higher voltage a less current is needed to produce the same power. The losses in the carrying cables are proportional to the square of current flowing, so conduction losses will be 4 times less in a 220V system compared to a 110V system. This gives the possibility to have longer range between the local downstep transformer (for example one which takes 20kV and converts them to 220V) and the end-user.