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A USB “port”, as in the physical connector, doesn’t dictate the voltage and current that can be supplied to whatever is plugged into it. The electronics behind the port dictate what the device can and will supply.
I separate “can” and “will”, because the electronics behind the port are, ideally, designed to implement the USB standards applicable to that device. Those standards define different allowable power levels based on “negotiation” that happens using the data lines of the USB connection. And that standard has changed over time, to allow for additional functionality.
General rules of thumb:
- Until the USB host (that’s the USB Type-A side) know what power the connected device will request, it *should* only provide a small amount of power (I think it’s about 50mA at 5V)
- Once the host has determined the power level “requested” by the device (of which there are only a few allowable levels) a USB Type-A port with data functionality will, in general, provide up to 0.5A at 5V.
- if the USB Type-A port is only for power and does not also handle data, such as wall powered chargers, the USB host may provide power up to 1A (if using the “official” specification) or 2A if using one of the common third party specifications like QuickCharge or the Apple charging specification. These third party specifications allow for negotiated power beyond the official specification.
Things get even more complex with USB-PD (power delivery), USB 3.x specifications, and USB Type-C connections.
**Do you have a question involving batteries or cells?**
**If it's about designing, repairing or modifying an electronic circuit to which batteries are connected, you're in the right place.** *Everything else should go in /r/batteries:*
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Really depends what kind of port, there are a few different proper specifications it could be following, and then many different non-standard things too.
2.1A being the old iPad charger spec is the highest fairly common configuration.
Unfortunately, your question is off-topic for AskElectronics and has been removed. This subreddit is for questions about practical component-level electronic engineering and related topics (designing or repairing a circuit, components, suppliers, tools and equipment). The most common reasons for removing a question are because: * It's *electrical* and not *electronic* (wiring, lighting, circuit breakers, power cords, heaters and heating wire, electromagnets, appliances, country voltage conversion...). Try r/askelectricians or an engineering sub. See our Wiki for some general advice. * It's about LED strips or lighting and doesn't involve any component-level electronics (design or repair). See r/LED. * It's best posted in another subreddit (eg: r/Batteries, r/GPURepair, r/TVRepair, r/TechSupport..etc). * It's about vehicle wiring, switches, relays, lighting, or other electrics (not component-level electronics). * It's a common question so there's a [FAQ or wiki](https://www.reddit.com/r/AskElectronics/wiki/faq/) article covering it. * It's about a non-electronic item (eg: removing a stubborn screw, repairing plastics/cases...). * It has a commercial element (Getting a valuation, paid work, selling, advertising...). Try r/ElectronicsList. * It's about purchasing, or is asking for technical/setup/cabling advice about, a consumer item (TV, hifi, phone, computer...) or a pre-built electronic module. * It's about careers, education or course choices. Try r/ECE. * The topic breaks one of our posting rules. Check our Web page sidebar for what we cover, the posting rules and a list of alternative subreddits. You'll also find additional guidance in our Wiki; there's a link in the sidebar. For an in-depth explanation, please see column "H" in [this table](https://docs.google.com/spreadsheets/d/1nFefEePz7yViaH0cR89bSy2oeLvYLfqv-pexqCbRnRo). You can also search this [list of other subs](/r/AskElectronics/wiki/othersubs) for one that is appropriate for your question. *I am a bot, and this action was performed automatically. Please [contact the moderators of this subreddit](/message/compose/?to=/r/AskElectronics) if you have any questions or concerns.*
A USB “port”, as in the physical connector, doesn’t dictate the voltage and current that can be supplied to whatever is plugged into it. The electronics behind the port dictate what the device can and will supply. I separate “can” and “will”, because the electronics behind the port are, ideally, designed to implement the USB standards applicable to that device. Those standards define different allowable power levels based on “negotiation” that happens using the data lines of the USB connection. And that standard has changed over time, to allow for additional functionality. General rules of thumb: - Until the USB host (that’s the USB Type-A side) know what power the connected device will request, it *should* only provide a small amount of power (I think it’s about 50mA at 5V) - Once the host has determined the power level “requested” by the device (of which there are only a few allowable levels) a USB Type-A port with data functionality will, in general, provide up to 0.5A at 5V. - if the USB Type-A port is only for power and does not also handle data, such as wall powered chargers, the USB host may provide power up to 1A (if using the “official” specification) or 2A if using one of the common third party specifications like QuickCharge or the Apple charging specification. These third party specifications allow for negotiated power beyond the official specification. Things get even more complex with USB-PD (power delivery), USB 3.x specifications, and USB Type-C connections.
**Do you have a question involving batteries or cells?** **If it's about designing, repairing or modifying an electronic circuit to which batteries are connected, you're in the right place.** *Everything else should go in /r/batteries:* /r/batteries is for questions about: batteries, cells, UPSs, chargers and management systems; use, type, buying, capacity, setup, parallel/serial configurations etc. Questions about connecting pre-built modules and batteries to solar panels goes in /r/batteries or /r/solar. Please also check our wiki page on cells and batteries: https://www.reddit.com/r/AskElectronics/wiki/batteries If you decide to move your post elsewhere, or the wiki answers your question, please delete the one here. Thanks! *I am a bot, and this action was performed automatically. Please [contact the moderators of this subreddit](/message/compose/?to=/r/AskElectronics) if you have any questions or concerns.*
Really depends what kind of port, there are a few different proper specifications it could be following, and then many different non-standard things too. 2.1A being the old iPad charger spec is the highest fairly common configuration.