Wiring to an SMPS secondary (before the rectification and filtering) would be only slightly better than a spark gap transmitter...
Depends on type. All of them will have sharp waveforms (read: tons of harmonics). Your antenna coupling network will require a strong lowpass or bandpass filter to deal with these. None of them are crystal controlled, so you won't be able to keep a, say, 500Hz CW channel (or whatever they're allocated as, at frequencies down there) tuned in. And many of them aren't fixed at all, where the switching frequency depends on load and component values rather than a fixed (e.g. RC timer) reference -- and wildly so, far more than you'll be able to hold a, say, NBFM (couple kHz) channel (if such are permitted in the band at all, which I'm guessing not..?).
So, in very, very broad strokes, yes, it's sort of how a high-efficiency (class D) transmitter works... But it's missing 110% all the subtle things to make an actual transmitter: there's no coupling network, it's not filtered, it's not modulated, it can't stay in its channel... take your pick!
Ed: incidentally, SMPS are over that frequency nowadays. Probably the cheaper and older models are still under 150kHz (FCC Part 15 lower threshold, so they only have to worry about levels of harmonics), but the newer and more compact types are pushing 300kHz, even low MHz with GaN FETs.
Tim