How to choose charger block accordingly

Hi all
Here is another question
How to choose the suitable charging block

I use the original 61w usb c charger for my MacBook Pro
And use a 5v-2.5A /9v-1.5A usb3 for my wireless charging pad for iphones
But I noticed although the pad is supporting 7.5-10w charge , the cable came with it that using is only usb2 to usbC

So im thining is 5v 2.5 A enough for the pad
Or getting a better cable ?
Or getting a usb c plus usb c to c cable?

And the other question is what is the risk of using a more powerful (36 or 61w) block for wireless pad or devices themselves

Thank you

SafeNsound=safe inside

2.5 watts is fine for iPad. Don’t worry about using a more powerful charger as your device will take whatever power it needs and not more. The charger will not provide too much power - think of the rating as a maximum.

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USB-C is somewhat special because it’s “smarter” and there is some ability to adapt to the device. If you want to be safest it’s best to stick to manufacturer recommendations as that is the only thing that was likely tested. The math is voltage * amperage == wattage. So as an example, if a 65W charger is asked to supply 12V, then the maximum amperage it could supply would be 65/12 = 5.4amps. In general the voltage is fixed, so in theory, as long as you have a power supply produces the correct voltage and produces enough wattage to supply at least the correct amperage, then it should be safe… if the cables are rated to work with the power levels. Remember there is a risk over overheating, device failure and ultimately fire if you do something wrong, so don’t get too creative.


Voltage is not fixed in USB-C PD and Qualcomm QuickCharge. It is negotiated by device and charger. All USB chargers will default to lowest common denominator of 5V. Current is variable depending on the device draw.


Usb c has a smart 9 or 5 v

But as my cables now have only usb 2 on one side so practically it only delivers the 2 amp meaning it is only a less than 10w power
So perhaps it is better for me to buy a usb c smart power blovk + a usb c to usb c cable and keep 61w MacBook Pro charger separate
Perhaps an original iphone 18w or an anker or belkin branded 36 or more would be fine

The only reason to get a new one is to consolidate your chargers. I have a four port charger that supplies 2 amps (at 5V) on each port. One of the ports is a QuickCharge 3.0 port (5V/2A, 9V/2A, 12V/1.67A) for supported devices (I use Samsung fast wireless charger on that port).

USB-C PD goes from 5 volts to 20 volts. To get higher wattage charging you may need special USB-C cables.

iPhone 8 upwards and newer iPads support USB-C PD for faster charging. I don’t have any USB-C chargers, but will charge a the high current of my 4 port charger (though not in the QC3.0 port).

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I sometimes use the 60W charger from my laptop for my smartphones, they auto-negotiate what they need.

I have asked here before about using my laptop chargers to charge the phone, but I still have never done so. So far, I still stick with the factory charger for all my devices - all 3 of my chrome devices and my phone. I still haven’t mixed anything yet


Thanks PHolder for explaining the relation between amperage and wattage. To confess my ignorance, I never knew amperage is wattage divided by voltage. I appreciate it.

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The physicists would use the formula



power = amperage x voltage

I couldn’t find a great Wikipedia entry, but there’s this


thanks again for the information

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That takes me back :slight_smile: Working in software, I don’t need to make those calculations that much, but when I was an engineering student had to work with those calculations all the time for DC circuits. AC power calculations is rather more complex.

Yeah i have a hand in technical electrical as well

Today i was checking some blocks i had
And noticed the one labled as 5v9v12v
Only has a usb2 jack with 4 pins 2power and 2 data(idle)

So correct me if im wrong but even though it is QC3.0 im not sure if thats capable of delivering the right voltage and power

My question is if anyone has the pin mapping for power and data for usb3.0 and usb c thunderbolt jacks
And if power pins in usb2 is capable of delivering variable voltages of it that should be rated only for 5v

What us the QC3 pd

That would most likely be a QuickCharge 3.0 charger. What is the current delivery (amperage) Multiply with the voltage to get yout power in watts. QC3.0 is not compatible with USB-C PD as they use different protocols to negotiate the voltage.

Most Android phones will support QC and newer ones will also support USB-C PD. My Samsung fast wireless charger requires a QC charger to deliver fast wireless charging.

I’ve said before that USB charging is a mess. Once everything supports USB-C PD then life will be easier.