1. your typical 240 Vac when rectified will be 240 x 1.41 =338.4 Volts DC. But if line goes up to 250 then 250 x 1.41 = 352.5!

So watch out.

2. RMS is that AC voltage that represents the same thermal effect when an equal DC voltage is applied to the load. That is if your line is 240Vac and you put a resistor on the line, that resistor will get hot. If you then apply DC voltage, you have to apply exactly 240 Volts to have the same thermal effect.

BUT note that 240Vac is not the maximum level that the line reaches. Is the peak of the sinus wave form and is 240x1,41.

Ioannis