Did the charger smoke, or the crappy included wires?
First replace the wires. The ones who come with these cheap power supplies are total junk. You won't be the first one having very low amps and hot/melting cables.
Get some proper cables.
I also recommend connecting the wires 'cross wired', the positive to the left top terminal and the negative to the bottom right terminal (with the screw). This compensates for voltage drop between the busbars, otherwise the most right cell will have (very minimal) lower voltage compared to the left cell since the busbars and connections add some voltage drop, just as
@jwelter99 mentioned.
As for the reversed polarity: This might have damaged the charger. You might have been lucky also, if it was only a diode on the output which now is toast, it doesn't mean the supply is toast. Just check with a multimeter and a car bulb to see if its still working.
Please note: 5A for topbalancing 4x280Ah is going to take forever.
Assuming the cells are at 50% SOC when arrived you need to top-up about 600Ah. With only 5A this will take at least 120 hours (5 days)
Not sure if those cheap chargers like to run at max load continously for so long, you might need to go down to 4A (adding even more time to finish)
I'd suggest getting a charger with some more amps, or serie-wire them
with a BMS set to 3.65V HVD and charge with a regular charger till the first cell hits HVD, rewire to parallel and finish topbalance. In that case you only need to top-balance from 99% to 100% SOC or so, since all cells are full, or near full.
Charging with 20A in series, and 50% SOC upon arrival requires you to put 120Ah in, thus taking approx 6 hours. Add 2-3 hours (depending on the cell drift) to finish topbalancing and you're good to go.
I personally don't like topbalancing unattended. So 5 days of continously charging equals to a few weeks if you don't want to leave it charging overnight