Will any micro USB charger work on a smartphone with a micro USB port, or should you only use the one that originally came with your smartphone? You’ll probably notice that some of these other chargers have slight differences on the margins. The amperage and voltage, for example, vary slightly from charger to charger. Does it really make any difference at all which one you use?
In terms of warranty, your smartphone manufacturer can deny a claim if they find out you used a non-OEM micro USB charger and it damaged the device. That’s the only real reason that smartphone companies recommend that you use their factory produced chargers. Third party chargers are fine as well, just as long as they meet the requirements of the smartphone’s original OEM charger. Most micro USB chargers are rated for 5.1V output, but the general rule is to just make sure that the mA rating is at least the same as the smartphone’s stock charger. If it’s any less, you’ll burn out the micro USB charger, and risk damaging your smartphone. I’ve personally had this happen to me in the past, although it thankfully did not harm the actually phone.
You might also want to think about possibly getting a USB charger with a higher mA output rating than your OEM charger. The smartphone will only draw as much power as it needs, so it’s not like the charger will overpower the smartphone. It will let it stay cooler though (I’ve seen some OEM chargers get pretty warm). Think of it like a kid and an adult. The kid could be running full tilt and hold a steady speed, but will tire quickly. The adult could go the same speed at just a fast walk, thus not working as hard and able to go longer without breaking a sweat. Electronics are the same way in that respect.
At the same time, you really get what you pay for. Try sticking with name brand (warranty backed) stuff. If you try to go with cheaper USB chargers, you risk getting the inferior parts. And the really cheap ones will not easily say what their power ratings are and you could get one that’s too weak a charger without even realizing it. I’ve seen two side by side on the shelf once. They looked exactly identical, only one was about $2 more than the other. At first I thought they were the same, just some put in the wrong place. I double checked the UPC and the numbers were different, which told me they were actually two separate items. I was able to look at the small sticker on the charger itself and turns out one was rated at 750mA (too little for my phone) and one was rated for 2.1 A. If I wasn’t a careful shopper, that could have been more than easily missed and go the wrong one because I wanted to save a couple bucks.