Yesterday I bought an el-cheapo charger off eBay for my new laptop - I always like to keep one in my briefcase for instant travel so I don't have to dismantle the rat's nest of wires under my desk (I have a spare laptop charger, phone charger, electronic ciggy battery charger and extension cable, along with sox, jox and a couple of shirts).
Plugged it in to test it and for some reason I couldn't get on the Net. Phoned BT Broadband, as I naturally assumed there was something wrong with the service, especially as it affected every wi-fi device attached to my home network.
After much mucking about and resetting of the router, the Indian gentleman from BT suggested I try a wired connection, so I unplugged the laptop from the charger and took it over to the router to connect a cable. Worked perfectly. That narrowed the problem down to the wi-fi.
BT man then made an adjustment to the wi-fi channel remotely; I unhooked the wired connection and it still worked perfectly. I gave BT man my thanks and rung off, took the laptop back to my desk, plugged in the charger and - the wi-fi had collapsed again.
Being in the microwave business myself, I suspected something was causing Radio Frequency Interference (RFI). It could only have been the laptop charger, which contains a transformer. I guessed the suppressor had failed.
Subsequent tests proved my theory - don't be tempted to buy cheap laptop chargers. Not only can they interfere with your wi-fi, they can also go up in smoke. Additionally, no amount of tin foil will create a Faraday Cage (I tried).