If you are sure the PSU can deliver 5.1V constantly or more (but not higher than 5.5V) under load then most likely the USB cable may be another source for the undervoltage. Search for "micro usb 24awg 2c". The AWG24 wire gauge allows up to two ampere. (cf. here). And pick the shortest you can get. It may fix the issue.

However, from theory this may still not enough for an RPI3 (rated 2.5A).
You may try this, but do it on your own risk: Power the Rpi3 via GPIO headers. This bypasses the voltage regulator of the microusb port, so only use a PSU which has a stabilized output. Caution: Any mistake in wiring will fry your Rpi.

Get or make two DuPont wires with female endings, either AWG24 or AWG22 Cut them apart, thus you have two for 5V and two for GND at the GPIO header Properly attach the DuPont wires to the PSU, note the polarity Attach the female endings to the respective GPIO headers (use 2x 5V and 2x Ground) (https://pinout.xyz/#), again note the polarity Make sure the wires do not losen during gameplay

@benjaminjay yeah, the official one: https://www.amazon.com/Official-Raspberry-Foundation-Power-Supply/dp/B01LCNF8FU

@Lolonois Thank you so much
this was the kind of information i was looking for (",)

i have seen this info a little later than i had hoped, but i just ordered myself one of these
https://www.ebay.co.uk/itm/F7A5-Output-5V-12V-24V-Switching-Power-Supply-Adapter-For-Arcade-Game/303072398956?_trkparms=aid%3D111001%26algo%3DREC.SEED%26ao%3D1%26asc%3D20160908105057%26meid%3D99aac9499dfb4225b56ee8f92564984a%26pid%3D100675%26rk%3D2%26rkt%3D15%26sd%3D132922393594%26itm%3D303072398956&_trksid=p2481888.c100675.m4236&_trkparms=pageci%3Ae5a0cda2-3c28-11e9-b0ec-74dbd180e49a|parentrq%3A3984c39f1690ab67099da24cfffd2b27|iid%3A1

As far as monitor heat extraction, no it wasn't something i had considered but now you've mentioned it, it's something i'll need to look into, so again thank you for your help and guidance i really appreciate you taking the time.

@mena Please don't hijack the original post. But to answer your question, most likely it will also protect the USB devices connected to it from power surges. These USB ports are meant to power or charge devices only and does not have data communication capabilities. USB devices such as USB keyboard/mouse, USB game controllers, etc will require both power and data and therefore have to be connected to the RPI USB ports and draw power from it as well.

@jay81uk simonster is right about the power requirements of various RPi models. So what is yours?
The Kindle Fire power supply normally will provide 1A current which 150ma more than the one from chromecast.

It turned out that I was just using a cheap ass micro USB cable, when I replaced it with a quality one the issue stopped happening, thanks anyways guys

Is there any you'd recommend? Modmypi.com where I usually buy my Pi stuff only seems to have up to 2.5A.