Number of devices supported by one outlet
Check Wikipedia's AC power plugs and sockets and identify the connector and current rating (amps or 'A')for your sockets.



Figure 1. French power socket. Source Wikipedia.

The relationship between power, voltage and current is very simple: \$P = VI \$ where P is power (watts or 'W'), V is voltage (volts or 'V') and I is current (amps or 'A).

For example, if your sockets are capable of 10 A then the maximum power you can draw is given by \$ P = VI = 220 \cdot 10 = 2200~W \$.