I went the easy route (and cheaper) by installing these.
Along with an inexpensive 4 Port POE+ switch with an uplink port. This handles 3 2K Dahua cameras and 1 5MP Panoramic Dahua camera without any bandwidth issues. It all comes back up after a power outage and is dead reliable. Of course, this only works if your garage AC circuit is on the same phase as the house AC circuit you plug the adapter into.
TL;DR: So if you're about to try a pair of PLA's, insure they comply with the G.hn specification.
Got nothing better to do or are curious:
I've used the old X-10's of the 80's and some of TP-LINK's PLAs over the years and they can work great but along with what you said, they must be on the same side of the phase (in the U.S., a split-phase, 120/240 3-wire residential service) in order to operate. If there's some capacitive coupling perhaps when a 240VAC device like an electric dryer or electric water heater is operating they may work marginally or still, not at all. So too often they just won't work or are troublesome for the application.
Enter the
G.hn spec for these PLAs circa 2012 where they claim to work on any wire in the house, same phase or not, and only caution about placing on a surge protector or next to "high powered electrical devices such as refrigerators, air-conditioners, microwave ovens, etc."
I cannot attest to how well these newer G.hn specs work but will likely have that opportunity soon. In the mean time, I posted this info in case someone is considering going with a pair of PLAs to solve an issue trying to provide Ethernet access to a remote barn or garage/shop that has power supplied by the house but have held back because it's not on the same leg/phase as the house and they couldn't get the PLAs to work (weren't of the G.hn spec).
So if you're about to try a pair of PLA's, insure they comply with the G.hn specification.
I can't specifically or personally recommend a device but I do know that Comtrend was on-board early and even has a version that provides POE. Also, zYxel has some G.hn-spec'd PLAs. I have an older pair of zYxel PLAs running in a customer's 2 story home for 6 years now without a hiccup.
Below are links to manufacturer info, both Comtrend and zYxel can be found at amazon and other online retailers.