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Hairdryers are capable of electrocuting people and are used in generally wetter conditions and run on mains power. Trimmers are used on dry bodies and use safe DC power from an adapter. Why are hairdryers not using adapters, especially when they are used in more dangerous conditions?

I can guess these reasons:

  • Trimmer cables are detachable from the body and harder to insulate
  • Trimmers have chargeable variants, so they are designed to run on DC
  • Trimmers will be unpleasantly heavy with integrated chargers
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  • $\begingroup$ Heating air requires quite a large amount of power and therefore voltage, so that is why it needs mains power. $\endgroup$ – fibonatic Jul 30 '16 at 10:43
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    $\begingroup$ A hairdryer needs about 1000x the power of a beard trimmer. It just isn't economically feasible to provide the electrical isolation needed at that power level. Therefore, different protections are used: double insulation and ground fault circuit interupters (residual current devices). $\endgroup$ – Dave Tweed Jul 30 '16 at 11:32
  • $\begingroup$ @DaveTweed I did a quick search and 40W laptop chargers could be cheaper than 40W hairdryers. And are ground fault circuit interupters part of the device? $\endgroup$ – Jesvin Jose Jul 30 '16 at 11:42
  • $\begingroup$ Where did you find a 40W hair dryer? Sounds rather useless. Sometimes GFCIs are built into the plug attached to the dryer, but more often, they're built into the bathroom wiring. $\endgroup$ – Dave Tweed Jul 30 '16 at 11:46
  • $\begingroup$ @DaveTweed my bad, I got the wrong figure. Turns out those cheap devices take 1 kilowatt. $\endgroup$ – Jesvin Jose Jul 30 '16 at 11:55
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This has nothing to do with safety. (At least in the U.S., the CPSC requires all hand-held hair dryers to have an integral GFI.)

Many trimmers on the market still run directly off line power.

Battery-powered/cordless trimmers are the only reason you will find any that use a power converter: The motor is built to run off of DC, provided by the on-board battery. The battery has to be charged from a DC supply.

You might find trimmers that do not feature batteries but to require a DC adapter. This is typically done when a manufacturer wants to produce a wired model, and realizes that it is cheaper to simply replace the battery and charging circuit with a transformer than to manufacture a separate AC motor.

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First, it's incorrect that beard trimmers always use some adapter between them and line power.

However, the main reason for hair dryers not using adapters is the large power they require. At 1 to 2 kW, a separate DC power supply would be large and expensive. At such power, you want to use the line voltage directly to minimize the current. Lower voltage would require higher current at the same power.

It is cheaper and better for the user to make the hairdryer safe to use line power, than to push the safety issues onto a separate power supply.

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