How do i know my PSU working well with GPU?

What does "I just heard if PSU is low enough to power GPU then melts" mean?

Monitor your PSU voltages using your motherboard utility software ( eg ASRock AXTU) or eg HWInfo - Sensors.

A good PSU will hold voltages with 0.2V of the target voltage.
 
You can check on PSU label how much have Amperes can supply on 12V rail.

Example if PSU have 40A * 12V = 480W now you must check how much your entire PC drain from 12V, add power consumption CPU + GPU + 50W-100W rest PC parts + 20-25% safety margin.

And check if your PSU is ratted on Tier list best are 1,2 , 3 is for low budget , and 4 for office use ,5 avoid.

http://www.tomshardware.co.uk/forum/id-2547993/psu-tier-list.html