Can all these USB powered gadgets damage your PC or power supply?

With Christmas around the corner I'm getting lots of questions from my users if they can give each other gifts of gadgets that connect to their USB ports for power. The "hot" one this year is heated mittens that plug in to the USB port. I have not previously set a policy on this and would rather not globally disable people's USB ports. Can anyone weigh in on if allowing users to power such devices like these, mini fridges, massagers, vacumes, etc., etc. cause any damage from constant use or should I just be more open minded? I hate to be a crab but I hate to also fry a couple hundred power supplies just so folks have something to put in their Christmas stockings!

If you think there is a negative impact and can cite a reference that would be great.
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data110Connect With a Mentor Commented:
I think that over time they could cause the USB ports to longer function. I don't believe they would cause any power supply issues. check this link out it might help you to decide.

USB Power
The USB specification provides a 5 V (volts) supply on a single wire from which connected USB devices may draw power. The specification provides for no more than 5.25 V and no less than 4.75 V (5 V±5%) between the positive and negative bus power lines.[9] Initially, a device is only allowed to draw 100 mA. It may request more current from the upstream device in units of 2 mA up to a maximum of 500 mA.

If a bus-powered hub is used, the devices downstream may only use a total of four units  400 mA (i.e. 2 watts)  of current. This limits compliant bus-powered hubs to 4 ports. The host operating system typically keeps track of the power requirements of the USB network and may warn the computer's operator when a given segment requires more power than is available.

On-The-Go and Battery Charging Specification both add new powering modes to the USB specification.

Some USB devices draw more power than is permitted by the specification for a single port. This is a common requirement of external hard and optical disc drives and other devices with motors or lamps. Such devices can be used with an external power supply of adequate rating.

As of June 14, 2007, all new mobile phones applying for license in China are required to adopt the USB port as a power port.[10]

In September, 2007 the Open Mobile Terminal Platform --a forum dominated by operators but including manufacturers such as Nokia, Samsung, Motorola, Sony Ericsson and LG--announced that its members had agreed on micro-USB as the future common connector for mobile devices. [11][12]

Not likley to fry a powersupply, but could easily overload and fry the USB port . .
if you fear for overloading, add a powered USB hub to the gifts, or a warning
and if you fear for the power supply, let them check the power you need here :
jmathesoAuthor Commented:
Thanks. That's the first link I've seen where somoone (even if it is Wikpedia) has been willing to step up and say these devices, especially the ones with multiple connectors to grab more power, can be harmful.
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