Yes harmonics issues are possible if using cheap PSU's. However, most today have PFC - Power Factor Control - that mitigate the problem. Most will advertise if they have PFC and give a Power Factor rating. A perfect resistive load gives a PF of 1.0 and most PSU's will be around 0.85 to 0.9
Ahh k. Thanks gents. So I take it the Bitmain supplied PSU's have this as I recall their powerfactor is 0.95