Travelling with a laptop can be a confusing experience for the novice when it comes to international power outlets and telephone jacks. Visitors to London for YAPC::Europe should find this brief document helpful in determining if the power supply on their laptop is capable of handling the voltage in the UK and what various adapters will be required.
Locate your laptop powerbrick and find the line that says "input". If your laptop is rated for international use you will see
INPUT: 100-240V 50-60Hz
Most European countries use 50Hz whereas the US uses 60Hz. Also, the voltage in the UK is 220-240Volts.
If your laptop is NOT rated, you will see something like
INPUT: 120VAC 60A
You may not use this device in the UK without a different powerbrick or a voltage transformer of some sort.
Even if you have a dual-voltage powerbrick for your laptop, many of your peripherals are likely not ready for world travel.
CHECK EACH AND EVERY TECH TOY DOO-DAD YOU PLAN TO BRING LEST YOU FRY IT OR NEED IT ONLY TO FIND YOU CANNOT USE IT!!!
If you have such unfit items and cannot find a dual-voltage brick for them you can get step-down transformers for them but I can attest to them being heavy, cumbersome and not terribly fun to travel with. Ditch the ancient hardware and get with the millenium. :)
Voltage Valet carries converters and transformers. Pay attention to whether or not it is'solid state' or not as you will want a transformer for anything electronic.
Power outlets and telephone jacks in the UK are different from those in the US and you will require a plug adapter to be able to plug your laptop into the wall. Most laptop and other appliances are 2 prong ungrounded plugs and will work with a variety of adapters availble from places such as your local RadioShack. If you don't have time to rip yourself away from the CRT long enough to peruse the shelves at RadioShack, I can recommend Voltage Valet or Teledapt for all your plug and phone jack needs.
If you have an ISP with international POPs, it would be a good idea to note the dial-up numbers now and configure your software for the trip and also write it down on a notecard as a back-up. Your modem will not recognise the dial tone so be sure to set your software to dial without tone. Also, either buy a tester or ask the hotel if the telephone lines are analog or digital before blithely plugging your modem in and zorching it to a crisp.