What exactly makes a group a "power trio" in your opinion?

Not when they’re also playing keyboards.

It’s not hard - drums+electric bass+electric guitar. One or more of those 3 sing (or no-one does). That’s it.

Upright bass? Not a PT. Acoustic guitar? Nope. Hell, if the drummer adds bongos, they’re no longer a power trio to me.

Perfect example. I’d add the Police as well.

Think of all those 70’s rock bands (and going into the 80’s in some cases) which had a designated vocalist. The singer was not always there to perform lyrics, but to be the fourth (or fifth) instrument, especially when you listen to live performances. Check out any number of YT clips of LZ performing Whole Lotta love. The same goes for Deep Purple (Gillan), Who (Daltrey), Van Halen (Diamond Dave era), U2 (Bono) early Guns’n’Roses.

A trio is three musicians. Full stop. A power trio is guitar, bass, drums. If there’s singing, it’s handled by one of the three musicians, e.g. Billy Gibbons and Sting.
ETA:

It is if it’s the Police. Though videos and photos of Sting with upright bass might be just for show.

If a group is described as a string quartet, would you feel cheated if they showed up with two violins, a cello, and a singer?

Suspended or truncated?

Not when Sting’s actually playing it. But generally, he played just a bass guitar, at least live. But also, they often played keyboards.

I think one thing is that some bands are always power trios, others act as power trios for some songs, and not for others.

How many ways Zeppelin split the take?

How many ways did ZZ Top?

OK, then.

Money is the answer to all questions.

Yes. If they were billed as the Skokie Illinois String Quartet. Because I’d expect a certain genre of music, and with a singer that ain’t it.

May the ghost of Buddy Holly haunt you forever.

The baritone was a big fat guy, like, orca fat.

Since they were a quartet, I think @MrDibble is safe from hauntings

the band line-up at the time: Holly on lead vocals and lead guitar, Niki Sullivan on rhythm guitar, Jerry Allison on drums, and Joe B. Mauldin on bass.

You’re mixing them up with the Skokie Illinois Polka Quartet.

Barbershop

I used to be in a barbershop quartet in Skokie, Illinois. The baritone was this guy named Kip Diskin, big fat guy, I mean, like, orca fat.

Planes, Trains and Automobiles? Uncle Buck? But it was John Candy, right?

Usual Suspects.
Verbal Kint

Apparently someone isolated exactly that quote.

Probably “Diminished”

Read your link:
“Sullivan dropped out after a little more than one year to resume his education. The Crickets, now a trio, continued to make stage and TV appearances and recorded more songs, many composed by the band members.”

Yes! That’s the word I was looking for! I get my sus and dim chords mixed up all the time.

I love power trios. Every person in the band must play something. No slacking!

One of my favorites is a somewhat obscure band from Wales called Budgie. They sorta looked and sounded like Rush, and unfortunately the press kept comparing them to Rush. But they were not trying to copy them.

Blue Cheer is another power trio I like.

Had to skip right to the end here after seeing people define trio…
Every time I saw Motorhead I came to a point where I was simply overwhelmed and amazed that all of the sound that was physically pounding off of my chest was being created by just the three guys on stage. It sounded like way more SOUND than just three guys could make. It was amazing.
(Yes there were times when Motorhead had 2 guitar players, I’m talking about Motorhead as a trio.)

This is my definition as well. A fourth person singing would not make it a power trio as, well, they are no longer a trio.

Yep, only three members or it ain’t a trio. I’m flexible on the instrumentation, though. Rush is certainly a power trio, maybe the overlords of it. I’ve always thought of Emerson, Lake & Palmer as a power trio, too.