I am thinking of using one of these cheap USB Chargers (Power Plug) designed for charging things like smartphones and mp3 player from mains voltage. In fact there are very cheap ones (i.g. ebay hongkong for less than 1$) - and there are more expensive ones. So i decided to measure the voltage with only little load (only my arduino with a small blinking led demo). This is what i got:
Artwizz Power Plug international (5V/1A) -> 5.15V
Noname white (App.. fake) -> 5.15V
DEV (5V/1A) -> 5.07V
Huawei (5V/1A) -> 4.99V
Noname (5V 1A) -> 5.86V
Noname (5.5V 500mA) -> 5.66V
Noname (5V 500mA) -> 5.05V
So in fact most of them should work without any trouble but i am afraid that voltages like 5.86V or 5.66V are "healthy" for 5V Electronics... What do You think?
According to the spec of the FT232RL input voltage must be :
+1.8V to +5.25V supply to the UART Interface and CBUS group pins (1...3, 5, 6,
9...14, 22, 23). In USB bus powered designs connect this pin to 3V3OUT pin to
drive out at +3.3V levels, or connect to VCC to drive out at 5V CMOS level. This
pin can also be supplied with an external +1.8V to +2.8V supply in order to drive
outputs at lower levels. It should be noted that in this case this supply should
originate from the same source as the supply to VCC. This means that in bus
powered designs a regulator which is supplied by the +5V on the USB bus should
be used.
While sold to the consumer market at "chargers" those are not actual chargers. They are 5V supplies, typically switching. Switching supplies generally need a minimum load in order to properly regulate.
Measuring the voltage with no load applied won't give you an accurate result of what they can supply.