I have a 15 led 0,5m led strip (ws2812b). Since it's such a limited amount of leds, I'll try to power the strip with an old phone power adapter (5v / 750mA). I looked at the ws2812's data sheet and it says
Each RGB LED draws approximately 50 mA at 5 V with red, green, and
blue at full brightness
So that's 15 x 50mA = 750mA
I'll call that one tight, but won't it be all right because these leds are never gonna run full power all the time.
I think the LEDs can run full power if you want "white colour full power", this is the combination of R+G+B
Now, sinking full power from your power supply can result in various scenarios:
Most likely the PS will show a not so good load regulation and the output voltage will decrease, decreasing the current demand in the LED and finding an "equilibrium". Example 4.8V and the LEDs at full power on 4.7V will only sink 710mA (just an example)
If the power supply has an over current protection (below 750mA) the circuit will switch OFF and ON periodically.
Other... I mean, the PS can be labelled with a power ratings but this can be far away from the truth with lots of low quality PS.
Just try it. If it doesn't work, some solutions could be:
If you are driving the LED yourself, don't drive all of them at 100%
If the LED are driven by other hardware you can't change, just add a resistor in series with the LED strip to decrease the current demand.