There are always going to be situations where you need to charge up your phone but you don't have the bundled charger on hand—and Apple isn't bundling a charging block at all with the new iPhone 12 (though you still get a Lightning cable in the box).
So can you just plug any charger into your phone to juice it up, especially now that the vast majority of handsets support the same wireless charging and USB-C standards? The short answer is yes, but the long answer involves a bit more explanation.
The most common spec you'll see on a charger is the watts (W)—essentially how much energy the charger can push toward your phone at once. Tablets and laptops will typically have chargers with a higher W value, as they have bigger batteries to fill (don't be surprised if your phone charger won't work with your laptop).
How quickly your phone goes from zero to a hundred in terms of battery life depends on both the watts coming from the charger and the maximum number of watts your phone can take (which you should be able to find out with a quick web search). The new iPhone 12, for example, can handle up to 20 W.
So if you buy the official 20-W charger from Apple, it's going to juice up your iPhone 12 about four times faster than the official 5-W charger from Apple. (Note too that the 20-W model supports the bigger iPad tablets, whereas the 5-W model doesn't, for the reasons we've already explained.)
This applies to laptop ports as well—the latest MacBook Pros can output 10 watts of power from their Thunderbolt/USB-C ports, which means they beat 5-W chargers but can't compete with the 20-W models. That's assuming your phone can take up to 20 W, by the way. If it tops out at 10 W, the MacBook Pro and the 20-W charger will restore its battery level at the same rate.
If you want the fastest battery charge possible for your phone, you need the charger that supplies as many watts as your phone can handle at once. Most of the time—but not always—the charger that came bundled with your phone will fit the bill.
When it comes to "fast charging," this is a technology that different manufacturers adopt in different ways, and the standards usually don't cross over between brands. The latest OnePlus 8T, for example, supports 65-W fast charging—it basically splits the battery up into two internally and charges both halves simultaneously.
As with normal charging, to get the best results from fast charging you need both the charger and the phone to support it—you can't just plug the OnePlus 8T into any charger and see that full 65-W speed charging.
Wireless charging is a little bit different. Again, you'll see the charging speed measured in watts, though wireless chargers are slower than the wired versions. Fortunately, just about everyone has now adopted the Qi wireless charging standard, so you can plonk your phone down on any model you like. Speaking of which …
What Charger Can I Use?
As long as you're using the right cable or the right wireless standard (and it's difficult not to), you can use just about any charger with your phone. Modern-day handsets will regulate the power draw to keep the battery protected, so there's no danger of blowing up your phone by using a charger that's too powerful for it.
That said, be wary of using cheap, no-brand chargers, or chargers that have been sitting around for years, as they may not necessarily stick to the same safety standards as the rest. We're not saying all of these chargers are dodgy, but to be safe it's always worth going with a newer charger from a reputable manufacturer or accessories maker, even if it's a little bit more expensive.
The bottom line is that while just about any new-ish charger will work with just about any new-ish phone at this point, you won't necessarily see the maximum charging speeds or the most efficient charging rate if you're not using kit made by the same company.
As we alluded to above, this is particularly true when it comes to fast charging, as phone makers like to deploy their own standards and methods—for the maximum fast charging rates, you'll usually need to plug in the charger specifically made for your phone. Use other chargers if you need to, but the official charger when you can.
It's the same for wireless charging. As most docks and mats now use the same standard, they should work with just about every phone—though different phones are likely to charge up at different speeds if the dock and handset haven't been specifically designed for each other (the charging device documentation should explain all of this for you).
The exception—as is often the case—is Apple. Its new MagSafe charging standard, designed for the iPhone 12 in particular, uses magnets to hold it in place, and we wouldn't recommend using it on other phones (magnets and wireless charging aren't typically a good mix, and Apple will have performed some clever engineering tricks to get it to work properly on the iPhone 12).
Apple itself has gone on the record as saying the official MagSafe Charger is capable of interfering with the magnetic strips and chips inside credit cards, security badges, passports and key fobs, and that it might leave imprints on leather cases. If you're using one of these, proceed with caution.
MagSafe and the iPhone 12 aside, you don't have to tread too carefully when it comes to swapping between chargers and phones—modern hardware is built to cope with this sort of swapping safely. For the fastest charging times and best results though, stick to specific chargers designed for specific phones as often as possible.