Rather than buying an power supply cord with a disconnect switch, why not just unplug the one you have?
- You are gone for exactly 7 days (168 hours)
- The phantom/stand-by load is 50 W (sounds high to me)
- You pay $0.20/kWh
- A power supply cord with a switch would cost you $30
Then the phantom load will add up to 8.4 kWh, or $1.68 worth of electricity.
If the power supply cord costs more than that (including the time to find and buy it, if you choose to calculate the cost that way), then it makes sense to just unplug the one you already have when you leave and plug it back in when you return. To do this you spend perhaps two minutes in total. Two minutes saving $1.68 off your electricity bill is about $50 per hour, and that is taxed money. Two minutes saving $30 for a switched power cord is $900 per hour.
Now, if you do this regularly, it might make more sense to have a convenient switch. And I'd be among the first to argue that anything to reduce unnecessary electricity use is probably a good thing. But unless you are paying closer to perhaps $1 per kWh and/or have an extremely high phantom load, it doesn't make much sense financially to buy a power supply cord with a switch. And I for one don't go on week-long vacation trips very often.