Strange problems that might be due to wiring
You can't replace 15A outlets with 20A outlets, even if the breakers are 20A, without first ensuring that the entire cable run is of appropriate gauge (and material) for 20A use. Otherwise you risk setting fire to your home.

I would check the voltages at the outlets using a CAT-II rated multimeter. You could alternatively use something like a Kill-a-watt plug-in meter.

I would also investigate how to get the supply quality assessed over time for surges, spikes etc.

Some better-quality UPSs allow you to log voltage over time, and perhaps events like spikes or surges, on a connected PC.