[gizmo686]

The limiting factor for outlets is typically the wire, not the plug. A standard NEMA 14-30 plug that is often used here in the US for high power appliances like dryers and ranges can provide 24amps continous at 240V, for a total of 5760[0] watts. Electric water heaters typically run at around 4500 watts. If you need more power, NEMA 14-50 is available as well.

More capable options exist if needed, but I have never seen them in a residential setting.

[0] The 30 indicates that it supports a peak wattage of 30.