Power supply to Arduino

Hello

Thanks Grumpy
I=U/R... ok!

Why will you not use a transistor!!!!!

I don't know...
Please let me know why should use it, and please, recommend one.

So, if I use this relay with 168R, plus other one (eg:12V to have more Ampers to pass through >300W) I will have problems and blow up Arduino?

Relay 5V -> Relay 12V = Blow up

What do you recommend to actuate for example 2A, 220V to have >300W?

Thanks on advance
Best regards
Pedro Ferrer