confused about boiler plates on power adapters?
first yes the cheap ones are often poorly designed either using fake complacency labels or just barley making it to the standard that being said try to avoid using them
as for the usb standard it is 5V (this can vary within .25V due to component values not being exact) most computer motherboards supply a MAXIMUM of 500mA to usb ports it doesn’t mean it will always supply that. the device(s) attached to it determines the current draw, the same is true for wall adapters. they will be rated for 500mA 750 mA 1A or 1.5A etc. the important number is the voltage you want to be as close to 5V as you can, all devices have some form of voltage regulation to protect agents slightly high voltage, (if they don’t its simply bad design) the excess energy gets dissipated as heat android devices are normally ok with power consumption on stand by but when you start doing a lot of cpu heavy tasks and have all the bells and whistles going (gps, back light, wifi, lte, cell modem, etc) it starts drawing a lot of current (and making the phone hot) i have screen phones draw more than 1A with everything running (the battery still draining while plugged into a 1A rated power adapter)
remember kids kerchoff’s (how ever its spelled) current and voltage laws
in series circuit V1+V2+V3+…Vn = Vt and in parallel circuit I1+I2+I3…In = It
(usbs are parallel devices) there for I1+I2+I3…In = It so the max output for a desktop usb is 500mA and you have 1 device using 400mA the other can at most use 100mA or they will balance out depending on how greedy the little bastards are (wants all the electrons for them selves)
don’t believe me turn on a lot of lights in your house than start a freezer or air conditioner and you will see the lights momentarily dim (due to the high current draw from the compressor starting) the voltage will stay at 120 (220-240 for Europe) but the current will drop to the other devices (or blow a fuse)