Rob,
There ara number of issues with that power supply kit, not least of all tha fact that a transformer with a 24 v ac secondary is going to give something like 36 v dc across C1...
Plus there is around 5v across D7.... This is totaling some 40 plus volts powering the three op amps...These are TLO81's with a maximum supply of 36 across their supply terminals....Result?
Thecanswer to this problem is use op amps with a higher operating voltage or use a transformer with a lower secondary voltage....
To answer your transformer question, the voltage is too high, see the above....and the current rating too low to expect 3 amps from the power supply.....
If the shortcomings of the design are overcome, then a transformer with at least a va rating of 100 watts is needed....( dont forget the power supply is 'supposed ' to be good for 30 v x 3 A or 90 watts...realistically a 120 watt rated transformer is needed.....
If you want to run the power supply as designed, then go for a transformer with a lower secondary voltage.....but then that cant becallowed to go too low else the Negative voltage rail charge pump circuit wont give the designed voltage.....(C2,C3,R2 R3, D5/D6)