PC not powering up unless I hold down power button for few seconds (other issue as well)

i'm rather suspicious it's a power issue, it could be the power source having unstable surges, or the PSU, you should check both of them for any problems

p.s: the mobo needing to be reset each time is likely a safety measure by the hardware

If you're having the same problem with multiple motherboards... have you ever thought to inspect the PC Case? There could be a short on the front panel/power wiring... or the plug could be loose.

PSU makes variations on AC mains irrelevant. For example, connect an incandescent bulb to the same AC power receptacle. Voltage is just fine even if the bulb dims to 40% intensity.

Surge protector does nothing useful especially for intermttents.. It is only for a transient that results in total hardware failure. Obviously you do not have that type damage.

Power is defined by a power controller. Its many inputs (including some from the PSU) determines if and when power goes on or off. Only a digital meter can identify what the system (the many components of that power system) are doing. Even a power button is an input to the power controller. If the power controller does not like something, then it may ignore that pressed button. Power cycling is determined by that power contoller and inputs to that controller.

Greatest reason for fixing things is to learn basic diagnostic concepts - how to think through any problem. For example, normal is for a defective part to still boot or run a computer, communication system, automobile, etc. How to find that part before fixing anything. A digital meter, a minute of labor, and requested instructions to see the problem before fixing anything. The resulting numbers mean the fewer who actually know the power 'system' can say what is defective and what is good - without speculation (ie "it could be").

Unfortunately, some computer assemblers have no idea how computers work. So good parts are replaced until something works. Most start with the PSU. A consumer magazine created a minor problem in computers. Then took each to repair shops. Ended up with many new power supplies. And only a few techs fixed the actual problem.

So a benchmark. When he measures voltages to determine if a PSU has long been defective, then have him to provide each voltage number for each relevant wire - to three digits and in writing. You will not know what those numbers mean. But only the informed shops will even bother or know how to provide those numbers. And, of course, those numbers can only report a defect when the entire computer remains intact - not even one wire disconnected.

Another example: heat does not cause failures. Heat finds defective parts. A computer that works in a 70 degree F room and fails in a 100 degree room means computer semiconductors may be 100% defective. And may cause problems at 70 degrees months or a year later. Appreciate one important diagnostic concept. Defective parts (ie a PSU) can still boot and run a computer. Heat is a diagnostic tool; not a reason for failure. Honest answers come with perspective (ie numbers).

Defined previously was how to obtain help from the fewer who really know this stuff. Example also separates shotgunners from others who actually know how a computer works.

And finally, remember what determines when a computer power cycles and even when its CPU is allowed to execute: a power controller. Numbers from a meter using requested instructions report on that power controller - without disconnecting anything.