I want to put my led strip in my PC and control it with Arduino or ESP. Since led strip has 60 leds it's going to draw ~3.5 amps. I'm asking if anything would happen if I connect led strip to 20 amps molex cable of my PSU? I am already writing my code, and this is the only thing that I'm interested in. Thanks!
Both the power supply and the LED strip are fine with that, as long as
- you don't draw that from the standby power pin
- you don't give a signal to the LED strip while it's unpowered (WS2812 are notoriously unhappy with that)
- you supply the LED strip in multiple places (because the copper is too thin to transport 3.5A all from one end)
This question has been asked here so many times it is getting boring. A properly designed load will only draw the current from the power source that it needs. The power source, if it has greater current capacity than the load requires, is not going to somehow force the load to take five or six times the current that it needs. Assuming that everything stays at the proper voltage of course.
Think about your cell phone charger that you plug into the AC mains receptacle in your house. That receptacle can likely supply 15A at the mains voltage and yet the charger only needs maybe 0.1A or so. By plugging in your cell phone charger it does not explode due to the 15A capability of the receptacle.