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I bought an LG Optimus One phone a long time ago. The phone came with a USB 2.0 cable + wall adapter.

3 months ago, I bought a Galaxy Note 3. The phone came with a USB 3.0 cable + wall adapter. The wall adapter stopped working, however the 3.0 cable still works. (When I connect my Note 3 to the computer using the 3.0 cable, it works. But when I try charging my Note 3 using a wall outlet, it doesn't work).

My question is:

Since the wall adapter which came with my Note 3 stopped working but the 3.0 cable still works, is it okay if I charge my Note 3 with the USB 3.0 cable while the 3.0 cable is plugged into the wall adapter which my LG Optimus One came with?

Note: I didn't try it yet because I was afraid it might ruin the 3.0 cable.

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USB devices are designed to use a wide variety of voltages ranging from 500mA to 1500mA and have been standardized for quite some time. You can generally plug any USB device into any USB cable and into any USB port, and nothing will blow up. Using a more powerful charger should speed up battery charging, while using a less powerful one will just charge slower. A good resource for this topic can be found here.

As noted in that article, the only real concern is when charging an older phone with a newer charger, as the battery might not be able to handle the higher current. In your cause your using an older charger with a new phone, so your all good.

  • right, I'm not concerned about the phone. Is it okay for my USB 3.0 cable to be plugged into an old adapter? – user2719875 May 12 '14 at 19:04
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    Yes, as long as it's micro USB. Your Note 3 is micro USB so if it fits it will work. – nullmem May 12 '14 at 19:06
  • okay thanks.. if it does fit, then will I be getting my regular charging speed / power? (I've noticed that my Note 3 charges much faster compared to my LG Optimus One). So if I charge my Note 3 with a USB 3.0 cable which is connected to an old adapter, will it charge at the same speed as it was charging before (when I connected the 3.0 cable to the new adapter which came with the phone) or will the charging speed be reduced? – user2719875 May 12 '14 at 19:11
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    Your old adapter is probably 500mA, and will charge a bit slower than normal. – nullmem May 12 '14 at 19:14
  • Note that by “old” the article means pre-2007 or thereabouts, so, really, for most people it is irrelevant. – theUg Aug 9 '14 at 14:57
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nullmem gave an excellent answer, but I'd like to add that it's NOT ok to plug use any USB-C cable.

USB-C was created exactly to resolve the kind of issues nullmem describes in his answer -- different chargers supply different currents, and different devices can accept different maximum currents.

The USB-C spec tries to negotiate the highest safe amount of current that the device trying to charge can accept, that the device supplying the power can provide, and that the cable can carry. To know this, the cable has to be intelligent. Several low-grade cables not only don't respect the specification but have faulty wiring, and this has been widely reported since it made nerd news when a Google engineer fried their Chromebook port using a faulty cable.

See the excellent USB-C guide here and the USB-C peripheral test spreadsheet (cables, chargers, etc) here.

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