If your red power good LED is not on bright and steady during operation you have a weak power supply.
A Raspberry Pi3B will consume less than 1A if you are not running it too hard and only have basic USB peripherals (non-backlit keyboard, mouse, and a USB flash drive). Push the SoC hard or connect power hungry USB devices and you can easily go well over 1A and might even pull more than 2A. This is why a 2.5A PSU is recommended. I believe the internal polyfuse is rated around 2.6A, so while a PSU rated for more than 2.5A will work, it will not increase the power load capacity of the Pi3 (the polyfuse will cut power if you try to pull more than 2.6A through the system).
Computer USB 2.0 ports will typically output 5V @ 500mA (0.5A) which is not enough to run a Pi3 under much more than idle conditions. USB 3.0 ports can output up to 900mA, which *might* be okay for a lightly loaded Pi3 (but it's still not recommended).
Note that phone charger type power supplies may have poor voltage regulation and not maintain 5V under load. I have tested "5V/2.4A" chargers that dipped well below 5V at only a 1A load. A phone will charge at 4.5V, but that's not enough to run a Pi3. Another potential problem with phone chargers is they often require a micro-USB cable between the PSU and Pi computer, and many standard micro-USB cables have too much internal resistance to deliver the kind of power a Pi3 might require. The USB 2.0 power spec is 5V @ 500mA (5V/0.5A), so that's all some micro-USB cables are designed to deliver. Charging cables that come with smartphones and tablets will usually be better at delivering power. Look for a micro-USB cable with at least 24 AWG power wires, and preferably larger than that (lower AWG = larger wires, so 20 AWG is better than 24).
The official RPF Pi3 power supply is rated at 5.1V/2.5A and has built-in 18 AWG power wires.
My mind is like a browser. 27 tabs are open, 9 aren't responding,
lots of pop-ups...and where is that annoying music coming from?