A low cost "USB to 12V Step-up Power Module" can be used to run a 3G wireless router, from the USB socket of a laptop computer. This should work for other low power electronic devices, saving having to carry around several mains power adaptors and allowing devices to be run away from mains power from the laptop battery. It also allows running 12 Volt devices from the same USB mains adaptor used for 5 Volt devices.
The module is from Canton Electronics, and is sold on eBay for US $5.45 (including international postage). The module arrived in Australia within two weeks of ordering.
The module consists of a small circuit board attached to a USB plug. The board has two screw terminations for attaching the supplied 5.5mm DC plug, via a short cable. The screws on the board are very small and I had some difficulty loosening one of them to attach the cable. It is very important to get the polarity of the cable correct (red wire for "+" positive terminal, for a positive tip on the plug).
First I tried the module wil a USB plugpack, as I did not want to risk damaging my computer. The module provided 12.2 Volts, with no load (measured with a multimeter).
Connecting the supply to a Huawei D100 3G Router showed a load of 160 mA without the USB Modem installed. With the Huawei E220 USB wireless modem installed, the router shut down. But this was not a problem with the module, but the plug-pack, which cannot supply enough power. Plugging the module into my laptop, the router with modem drew 200 to 330 mA.
I left the module running all night and it was working fine in the morning and did not feel warm to the touch. The module has no case, so I wrapped it in self-amalgamating tape, to protect it.
There are a few improvements which could be made to the module. One would be to supply the module with the cable already attached. Another would be a case for the module. Also the cable could be a bit longer (the one supplied is about 300 mm), I suggest 500 mm (the same length as the shortest commonly available Ethernet patch cables).
One question I have with the module is what it is actually for. The maker's description says "Home Automation Solar charger". This does not make a lot of sense, as a solar panel is unlikely to be putting out 5 Volts, nor have a USB socket . If this was instead described as a "USB to 12 Volt power supply", provided with a case and a slight longer cable, it could be a popular unit.